diff --git a/BACKLOG.md b/BACKLOG.md
index db28395..c1c90a3 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -209,9 +209,13 @@ Split (issue #11 closed) into two independently-demoable slices per §13 — the
 
 #### S-10b · Real diploma upload stored via the ACL Documenten API — #103
 
-**Outcome:** the self-service "Documenten aanleveren" action becomes a real file upload; the document is stored in the ZGW Documenten (DRC) API and related to the zaak, with all document calls routed through the ACL (§8.1), and the zaak is set to a cancellation status on timeout expiry. Builds on the S-10a trigger/wait. Depends on #102.
+**Outcome:** the self-service "Documenten aanleveren" action becomes a real file upload; the file (base64-encoded end-to-end) is stored in the ZGW Documenten (DRC) API as an `enkelvoudiginformatieobject` and related to the zaak, with all document calls routed through the ACL (§8.1, ADR-0018). Builds on the S-10a trigger/wait. Depends on #102.
 
-**Acceptance:** ACL Documenten gateway integration test; Playwright e2e uploads a real document; the openbaar/zaak reflects the stored document.
+**Acceptance:** ACL Documenten gateway integration test (real OpenZaak); Playwright e2e uploads a real PDF.
+
+#### S-10c · Close the ZGW zaak on document-timeout expiry — #106
+
+**Outcome:** when the 30-day term lapses (S-10a `RegistratieVerlopen`), the ZGW zaak is set to a cancellation status (not just the domain aggregate → `Verlopen`). Adds a cancellation statustype/resultaattype to the seed + an ACL method + expiry-worker wiring. Carved from S-10b (ADR-0017/0018). Depends on #103.
 
 ### S-11 · Withdrawal (Flow 3)
 
diff --git a/apps/self-service/src/app/registration/registration-page.html b/apps/self-service/src/app/registration/registration-page.html
index 6910880..255dba4 100644
--- a/apps/self-service/src/app/registration/registration-page.html
+++ b/apps/self-service/src/app/registration/registration-page.html
@@ -19,11 +19,20 @@
               Het aanleveren van uw documenten is niet gelukt. Probeer het opnieuw.
             </p>
           }
+          <p utrecht-paragraph>Lever uw diploma aan (PDF).</p>
+          <label utrecht-form-label for="diploma">Diploma</label>
+          <input
+            id="diploma"
+            type="file"
+            accept="application/pdf"
+            [disabled]="providingDocuments()"
+            (change)="onFileSelected($event)"
+          />
           <button
             utrecht-button
             appearance="primary-action-button"
             type="button"
-            [disabled]="providingDocuments()"
+            [disabled]="providingDocuments() || !selectedFile()"
             (click)="provideDocuments()"
           >
             Documenten aanleveren
diff --git a/apps/self-service/src/app/registration/registration-page.spec.ts b/apps/self-service/src/app/registration/registration-page.spec.ts
index f17ff06..8e8cff9 100644
--- a/apps/self-service/src/app/registration/registration-page.spec.ts
+++ b/apps/self-service/src/app/registration/registration-page.spec.ts
@@ -83,21 +83,29 @@ describe('RegistrationPage', () => {
     expect(await screen.findByText(/ingetrokken/i)).toBeTruthy();
   });
 
-  it('offers to provide documents after submitting, and doing so confirms', async () => {
+  // A small PDF file the citizen "uploads"; the component base64-encodes it client-side.
+  const diploma = () => new File([new Uint8Array([1, 2, 3])], 'diploma.pdf', { type: 'application/pdf' });
+
+  it('uploads a chosen diploma after submitting, and doing so confirms', async () => {
     const { provideDocuments, providers: p } = providers();
     await render(RegistrationPage, { providers: p });
 
     fireEvent.click(screen.getByRole('button', { name: /indienen/i }));
     await screen.findByText(/ontvangen/i);
 
+    // Choose the file, then upload it.
+    fireEvent.change(screen.getByLabelText(/diploma/i), { target: { files: [diploma()] } });
     fireEvent.click(await screen.findByRole('button', { name: /documenten aanleveren/i }));
 
-    // The provide-documents call is keyed by the reference the submit returned, and the page confirms.
-    expect(provideDocuments).toHaveBeenCalledWith('reg-9');
+    // The upload is keyed by the reference and carries the base64 file + its name; the page confirms.
     expect(await screen.findByText(/documenten.*aangeleverd/i)).toBeTruthy();
+    expect(provideDocuments).toHaveBeenCalledWith(
+      'reg-9',
+      expect.objectContaining({ fileName: 'diploma.pdf', contentType: 'application/pdf', contentBase64: expect.any(String) }),
+    );
   });
 
-  it('surfaces a provide-documents failure and keeps the action available', async () => {
+  it('surfaces a diploma-upload failure and keeps the action available', async () => {
     const { providers: p } = providers(
       vi.fn().mockReturnValue(of({ registrationId: 'reg-9', status: 'Ingediend' })),
       vi.fn().mockReturnValue(of(undefined)),
@@ -107,6 +115,7 @@ describe('RegistrationPage', () => {
 
     fireEvent.click(screen.getByRole('button', { name: /indienen/i }));
     await screen.findByText(/ontvangen/i);
+    fireEvent.change(screen.getByLabelText(/diploma/i), { target: { files: [diploma()] } });
     fireEvent.click(await screen.findByRole('button', { name: /documenten aanleveren/i }));
 
     expect(await screen.findByRole('alert')).toBeTruthy();
diff --git a/apps/self-service/src/app/registration/registration-page.ts b/apps/self-service/src/app/registration/registration-page.ts
index 8c93c48..7d6a916 100644
--- a/apps/self-service/src/app/registration/registration-page.ts
+++ b/apps/self-service/src/app/registration/registration-page.ts
@@ -29,6 +29,7 @@ export class RegistrationPage {
   protected readonly providingDocuments = signal(false);
   protected readonly documentsProvided = signal(false);
   protected readonly provideDocumentsFailed = signal(false);
+  protected readonly selectedFile = signal<File | undefined>(undefined);
 
   submit(): void {
     this.submitting.set(true);
@@ -47,24 +48,44 @@ export class RegistrationPage {
     });
   }
 
-  provideDocuments(): void {
+  onFileSelected(event: Event): void {
+    const input = event.target as HTMLInputElement;
+    this.selectedFile.set(input.files?.[0] ?? undefined);
+  }
+
+  async provideDocuments(): Promise<void> {
     const reference = this.reference();
-    if (!reference) {
+    const file = this.selectedFile();
+    if (!reference || !file) {
       return;
     }
     this.providingDocuments.set(true);
     this.provideDocumentsFailed.set(false);
-    this.bff.postSelfServiceRegistrationsIdDocuments(reference).subscribe({
-      next: () => {
-        this.documentsProvided.set(true);
-        this.providingDocuments.set(false);
-      },
-      // Surface the failure instead of swallowing it: keep the action so the user can retry.
-      error: () => {
-        this.provideDocumentsFailed.set(true);
-        this.providingDocuments.set(false);
-      },
-    });
+    let contentBase64: string;
+    try {
+      contentBase64 = await readAsBase64(file);
+    } catch {
+      this.provideDocumentsFailed.set(true);
+      this.providingDocuments.set(false);
+      return;
+    }
+    this.bff
+      .postSelfServiceRegistrationsIdDocuments(reference, {
+        contentBase64,
+        fileName: file.name,
+        contentType: file.type || 'application/pdf',
+      })
+      .subscribe({
+        next: () => {
+          this.documentsProvided.set(true);
+          this.providingDocuments.set(false);
+        },
+        // Surface the failure instead of swallowing it: keep the action so the user can retry.
+        error: () => {
+          this.provideDocumentsFailed.set(true);
+          this.providingDocuments.set(false);
+        },
+      });
   }
 
   withdraw(): void {
@@ -87,3 +108,13 @@ export class RegistrationPage {
     });
   }
 }
+
+/** Read a file's bytes as a base64 string (without the `data:...;base64,` prefix). */
+function readAsBase64(file: File): Promise<string> {
+  return new Promise<string>((resolve, reject) => {
+    const reader = new FileReader();
+    reader.onload = () => resolve(((reader.result as string) ?? '').split(',', 2)[1] ?? '');
+    reader.onerror = () => reject(reader.error ?? new Error('Could not read the file.'));
+    reader.readAsDataURL(file);
+  });
+}
diff --git a/docs/architecture/adr-0018-diploma-upload-via-acl-documenten.md b/docs/architecture/adr-0018-diploma-upload-via-acl-documenten.md
new file mode 100644
index 0000000..4f97e68
--- /dev/null
+++ b/docs/architecture/adr-0018-diploma-upload-via-acl-documenten.md
@@ -0,0 +1,74 @@
+# ADR-0018: Diploma upload is stored in the ZGW Documenten API, fronted by the ACL
+
+- **Status:** Accepted
+- **Date:** 2026-07-20
+- **Deciders:** Respellion engineering
+- **Relates to:** S-10b (#103); proposal #107. Builds on ADR-0001 (ACL is the only ZGW caller),
+  ADR-0003 (ACL default-fill), ADR-0017 (document-wait + provision trigger). Carves the zaak-close on
+  expiry to #106 (S-10c).
+
+## Context
+
+S-10a wired the "documenten aanleveren" trigger (portal → BFF → domain → complete the WachtOpDocumenten
+wait) with the file itself stubbed. S-10b makes the upload real: the diploma must be **stored in the
+ZGW Documenten (DRC) API** and related to the zaak. §8.1 makes the ACL the only code that talks to ZGW.
+The DRC API is served by the same OpenZaak container as the Zaken/Catalogi APIs.
+
+## Decision
+
+**The ACL fronts the Documenten API: it creates an `enkelvoudiginformatieobject` and relates it to the
+zaak. The file travels base64-encoded in JSON across every hop (the portal encodes it client-side); a
+"Diploma" `informatieobjecttype` is seeded in the catalogus and injected into the ACL like the
+zaaktype.**
+
+- **ACL gateway.** `OpenZaakGateway.StoreDocumentAsync` POSTs the `enkelvoudiginformatieobject`
+  (`/documenten/api/v1/enkelvoudiginformatieobjecten`, base64 `inhoud`, `bestandsomvang`,
+  `status=definitief`) then relates it to the zaak (`/zaken/api/v1/zaakinformatieobjecten`), reusing the
+  established gateway patterns (ZGW Bearer JWT, buffered non-chunked body for uwsgi, **no CRS headers** —
+  the Documenten API is not geo, unlike zaak-create). `AclService.StoreDiplomaAsync` default-fills the
+  ZGW-mandatory fields (informatieobjecttype, bronorganisatie, vertrouwelijkheidaanduiding, `taal=nld`,
+  creatiedatum); the domain hands over only the zaak, the bytes, and the file's name/type. No new ZGW
+  scopes were needed — the seed applicatie holds `heeft_alle_autorisaties`.
+- **The file travels as base64 JSON end-to-end.** The portal reads the chosen file client-side
+  (`FileReader`) and posts `{ contentBase64, fileName, contentType }` as JSON to the BFF; the BFF
+  forwards it to the domain, and the domain to the ACL, all as JSON. This deviates from proposal #107's
+  "multipart on the portal→BFF hop": base64 JSON keeps **one** contract shape across all four services
+  (no `IFormFile`/antiforgery plumbing, no multipart in the generated client), and a diploma is a small
+  placeholder PDF, so the ~33% base64 overhead is immaterial. The ACL turns the base64 back into the
+  ZGW `inhoud`.
+- **Storing precedes completing the wait.** `ProvideDocuments` (from S-10a) now stores the diploma via
+  the ACL — once the zaak is opened — and then completes the `WachtOpDocumenten` task, so a registration
+  reaches beoordeling only after its diploma is stored. Both steps stay best-effort about missing
+  preconditions (no zaak yet → skip storage; no process yet → skip completion), mirroring withdrawal.
+- **Catalogus.** `seed_catalogus.py` (OZ_PUBLISH) creates a "Diploma" `informatieobjecttype`, relates it
+  to the zaaktype (`zaaktype-informatieobjecttypen`, while both concept), publishes both, and prints
+  `INFORMATIEOBJECTTYPE_URL`; verify-domain injects it as `Acl__Defaults__InformatieobjecttypeUrl`
+  (a zeros-uuid placeholder otherwise, so the ACL still boots).
+
+## Consequences
+
+**Positive**
+
+- §8.1 stays intact: the ACL is still the only ZGW caller; the portal only talks to the BFF; the domain
+  only crosses the ACL boundary. Adding a document was almost entirely additive (one gateway method, one
+  default, one seed block).
+- One JSON contract shape across portal/BFF/domain/ACL keeps the generated client and the service
+  contracts uniform; the upload is exercised live (ACL integration test against real OpenZaak; the
+  Playwright journey uploads a real PDF).
+
+**Negative / costs**
+
+- Base64 inflates the payload ~33% and holds the whole file in memory at each hop — fine for a small
+  diploma, but not a pattern to reuse for large documents without streaming/multipart.
+- The zaak is **not** set to a cancellation status when the 30-day term lapses — carved to #106 (S-10c),
+  which adds the cancellation statustype/resultaattype + ACL method + expiry-worker wiring.
+- Providing documents before the zaak is opened silently skips storage (best-effort); the e2e/live flow
+  avoids this by uploading only after the openbaar register shows the zaak (INGEDIEND).
+
+## Alternatives considered
+
+- **Multipart on the portal→BFF hop** (proposal #107). Rejected: it splits the transport into two shapes
+  (multipart then JSON), needs `IFormFile` + antiforgery handling and a multipart method in the generated
+  client, for no benefit at diploma size.
+- **The domain talks to the Documenten API directly.** Rejected outright: violates §8.1 (only the ACL
+  talks to ZGW).
diff --git a/docs/demo-script.md b/docs/demo-script.md
index 7b48e0c..3004a40 100644
--- a/docs/demo-script.md
+++ b/docs/demo-script.md
@@ -434,3 +434,31 @@ routing → `Beoordelen`), OR the `P30D` interrupting timer fires → `Registrat
 > Both branches are covered by the `Een documenttermijn laten verlopen` acceptance scenarios (worker +
 > aggregate) and unit tests; the wait completion and the 30-day timer firing are asserted live by the
 > verify-domain check.
+
+## S-10b — Diploma upload stored in the ZGW Documenten API (#103, ADR-0018)
+
+The self-service "Documenten aanleveren" action (S-10a) is now a **real file upload**: after submitting,
+the citizen picks a PDF and uploads it. The portal base64-encodes the file client-side and posts it to
+the BFF; the BFF forwards it to the domain, which stores it via the **ACL** as a ZGW
+`enkelvoudiginformatieobject` in the **Documenten (DRC) API** and relates it to the zaak — then completes
+the `WachtOpDocumenten` wait so beoordeling can proceed. Per §8.1 only the ACL talks to ZGW.
+
+```bash
+make up
+# 1. Log in as jan-burger / test123, submit, then — once the openbaar register shows the row —
+#    choose a PDF under "Documenten aanleveren" and upload it. The page confirms "aangeleverd".
+open http://localhost:8140
+#
+# 2. Automated: the walking-skeleton e2e now uploads a real PDF before the behandelaar approves.
+make verify-e2e
+#
+# 3. The ACL integration test proves the document is really created in the Documenten API and
+#    related to the zaak (against a live OpenZaak):
+make verify-acl        # → "Storing a diploma creates a real informatieobject related to the zaak"
+```
+
+**The path:** portal (base64) → BFF `POST /self-service/registrations/{id}/documents` → domain
+`ProvideDocuments` → ACL `POST /documenten` → ZGW `enkelvoudiginformatieobjecten` +
+`zaakinformatieobjecten`; the wait is then completed and the case advances to Beoordelen (§8.1, ADR-0018).
+
+> Setting the ZGW zaak to a cancellation status on 30-day expiry is a follow-up (S-10c, #106).
diff --git a/infra/docker-compose.yml b/infra/docker-compose.yml
index 2529274..ce76cdf 100644
--- a/infra/docker-compose.yml
+++ b/infra/docker-compose.yml
@@ -306,6 +306,9 @@ services:
       Acl__Defaults__Vertrouwelijkheidaanduiding: openbaar
       # Override with the real zaaktype URL after running seed_catalogus.py.
       Acl__Defaults__ZaaktypeUrl: ${ACL_ZAAKTYPE_URL:-http://openzaak:8000/catalogi/api/v1/zaaktypen/00000000-0000-0000-0000-000000000000}
+      # The informatieobjecttype a diploma is filed under (S-10b). Placeholder until seed_catalogus.py
+      # (OZ_PUBLISH=1) reports the real URL, which verify-domain injects like the zaaktype URL.
+      Acl__Defaults__InformatieobjecttypeUrl: ${ACL_INFORMATIEOBJECTTYPE_URL:-http://openzaak:8000/catalogi/api/v1/informatieobjecttypen/00000000-0000-0000-0000-000000000000}
     ports:
       - "8100:8080"
     healthcheck:
diff --git a/infra/openzaak/seed_catalogus.py b/infra/openzaak/seed_catalogus.py
index 5dc15a8..ed4ad67 100644
--- a/infra/openzaak/seed_catalogus.py
+++ b/infra/openzaak/seed_catalogus.py
@@ -124,6 +124,58 @@ def publish_zaaktype(zt):
         print("skip   publish (already published)")
 
 
+def seed_informatieobjecttype(cat, zt):
+    """Create the "Diploma" informatieobjecttype and relate it to the zaaktype (both idempotent).
+
+    A diploma uploaded in S-10b is filed under this informatieobjecttype; OpenZaak only accepts a
+    document (and its zaak relation) once the informatieobjecttype is published AND allowed for the
+    zaak's zaaktype (a zaaktype-informatieobjecttype relation). Both the relation and this call must run
+    while the zaaktype is still a concept, so seed this *before* publishing the zaaktype. Returns the
+    informatieobjecttype dict.
+    """
+    iots = [i for i in find(f"/informatieobjecttypen?catalogus={cat['url']}&status=alles")
+            if i.get("omschrijving") == "Diploma"]
+    if iots:
+        iot = iots[0]
+        print(f"skip   informatieobjecttype Diploma ({iot['url']}) concept={iot.get('concept')}")
+    else:
+        st, iot = api("POST", "/informatieobjecttypen", {
+            "catalogus": cat["url"],
+            "omschrijving": "Diploma",
+            "vertrouwelijkheidaanduiding": "openbaar",
+            "informatieobjectcategorie": "diploma",
+            "beginGeldigheid": "2026-01-01",
+        })
+        if st != 201:
+            sys.exit(f"create informatieobjecttype -> {st}: {json.dumps(iot, indent=2)}")
+        print(f"create informatieobjecttype Diploma ({iot['url']})")
+
+    # Relate it to the zaaktype (must be done while both are concept).
+    relations = find(f"/zaaktype-informatieobjecttypen?zaaktype={zt['url']}&status=alles")
+    if any(r.get("informatieobjecttype") == iot["url"] for r in relations):
+        print("skip   zaaktype-informatieobjecttype Diploma")
+    else:
+        st, body = api("POST", "/zaaktype-informatieobjecttypen", {
+            "zaaktype": zt["url"], "informatieobjecttype": iot["url"],
+            "volgnummer": 1, "richting": "inkomend"})
+        if st != 201:
+            sys.exit(f"relate zaaktype-informatieobjecttype -> {st}: {json.dumps(body, indent=2)}")
+        print("create zaaktype-informatieobjecttype Diploma")
+
+    return iot
+
+
+def publish_informatieobjecttype(iot):
+    """Publish the informatieobjecttype (idempotent) so documents may reference it."""
+    if iot.get("concept", True):
+        st, body = api("POST", f"{iot['url']}/publish")
+        if st != 200:
+            sys.exit(f"publish informatieobjecttype -> {st}: {json.dumps(body, indent=2)}")
+        print(f"publish informatieobjecttype Diploma ({iot['url']})")
+    else:
+        print("skip   publish informatieobjecttype (already published)")
+
+
 def main():
     # 1. Catalogus
     existing = [c for c in find(f"/catalogussen?domein=BIG") if c.get("domein") == "BIG"]
@@ -198,10 +250,16 @@ def main():
     # schema-mandatory" zaaktype S-01 asks for (ADR-0002). Set OZ_PUBLISH=1 to add
     # those relations and publish — needed so a real zaak POST is accepted, which
     # the ACL integration test (S-04a, #46) exercises. See ADR-0006.
+    iot = None
     if PUBLISH:
         # Re-fetch: the bsn-eigenschap branch above may hold a stale concept flag.
         zt = next(z for z in find(f"/zaaktypen?catalogus={cat['url']}&status=alles")
                   if z.get("identificatie") == "BIG-REGISTRATIE")
+        # Seed + relate the Diploma informatieobjecttype (S-10b) while the zaaktype is still concept,
+        # then publish both. Publish the informatieobjecttype before the zaaktype so the zaaktype's
+        # relations reference a published type.
+        iot = seed_informatieobjecttype(cat, zt)
+        publish_informatieobjecttype(iot)
         publish_zaaktype(zt)
 
     # 5. Verify the JWT client can list the zaaktype (concepts included).
@@ -214,6 +272,10 @@ def main():
     # zaaktype URL to configure the ACL's default-fill (ADR-0003/0009).
     zt_url = next(z["url"] for z in zaaktypen if z.get("identificatie") == "BIG-REGISTRATIE")
     print(f"ZAAKTYPE_URL {zt_url}")
+    # Machine-readable informatieobjecttype URL (S-10b) so callers can configure the ACL's document
+    # default-fill. Only emitted when publishing — a concept informatieobjecttype can't back a document.
+    if iot is not None:
+        print(f"INFORMATIEOBJECTTYPE_URL {iot['url']}")
     print(f"OK — BIG catalogus seeded (BIG-REGISTRATIE {state} + bsn eigenschap)")
 
 
diff --git a/infra/run-domain-check.sh b/infra/run-domain-check.sh
index 7294c54..359f65c 100755
--- a/infra/run-domain-check.sh
+++ b/infra/run-domain-check.sh
@@ -33,13 +33,18 @@ echo ">> openzaak=$oz_ip domain=$dom_ip network=$net"
 echo ">> seeding a published BIG zaaktype (idempotent) and capturing its URL"
 sid="$(docker create --network "$net" -e "OZ_BASE=$oz_base" -e OZ_PUBLISH=1 python:3-slim python /seed.py)"
 docker cp "$here/openzaak/seed_catalogus.py" "$sid:/seed.py" >/dev/null
-zt_url="$(docker start -a "$sid" | sed -n 's/^ZAAKTYPE_URL //p' | head -1)"
+seed_out="$(docker start -a "$sid")"
+zt_url="$(printf '%s\n' "$seed_out" | sed -n 's/^ZAAKTYPE_URL //p' | head -1)"
+iot_url="$(printf '%s\n' "$seed_out" | sed -n 's/^INFORMATIEOBJECTTYPE_URL //p' | head -1)"
 docker rm -f "$sid" >/dev/null
 [ -n "$zt_url" ] || { echo "ERROR: seed did not report a ZAAKTYPE_URL" >&2; exit 1; }
+[ -n "$iot_url" ] || { echo "ERROR: seed did not report an INFORMATIEOBJECTTYPE_URL" >&2; exit 1; }
 echo ">> zaaktype: $zt_url"
+echo ">> informatieobjecttype: $iot_url"
 
-echo ">> recreating the acl service pointed at the seeded zaaktype (host-consistent)"
-ACL_ZAAKTYPE_URL="$zt_url" ACL_OPENZAAK_BASEURL="$oz_base/" docker compose -f "$compose" up -d acl
+echo ">> recreating the acl service pointed at the seeded zaaktype + informatieobjecttype (host-consistent)"
+ACL_ZAAKTYPE_URL="$zt_url" ACL_INFORMATIEOBJECTTYPE_URL="$iot_url" ACL_OPENZAAK_BASEURL="$oz_base/" \
+  docker compose -f "$compose" up -d acl
 WAIT_TIMEOUT="${WAIT_TIMEOUT:-120}" bash "$here/wait-healthy.sh" acl
 
 echo ">> submitting a registration to the domain"
diff --git a/libs/api-client/src/lib/generated/bff-api.ts b/libs/api-client/src/lib/generated/bff-api.ts
index f5d35d7..3ac28e9 100644
--- a/libs/api-client/src/lib/generated/bff-api.ts
+++ b/libs/api-client/src/lib/generated/bff-api.ts
@@ -35,6 +35,14 @@ export interface OpenbaarEntry {
   reference: string | null;
 }
 
+export interface ProvideDocumentsRequest {
+  contentBase64: string;
+  /** @nullable */
+  fileName?: string | null;
+  /** @nullable */
+  contentType?: string | null;
+}
+
 export interface SubmitAccepted {
   registrationId: string;
   status: string;
@@ -226,15 +234,19 @@ export class BffApiV1Service {
     );
   }
 
- postSelfServiceRegistrationsIdDocuments<TData = void>(id: string, options?: HttpClientBodyOptions): Observable<TData>;
- postSelfServiceRegistrationsIdDocuments<TData = void>(id: string, options?: HttpClientEventOptions): Observable<HttpEvent<TData>>;
- postSelfServiceRegistrationsIdDocuments<TData = void>(id: string, options?: HttpClientResponseOptions): Observable<AngularHttpResponse<TData>>;
+ postSelfServiceRegistrationsIdDocuments<TData = void>(id: string,
+    provideDocumentsRequest: ProvideDocumentsRequest, options?: HttpClientBodyOptions): Observable<TData>;
+ postSelfServiceRegistrationsIdDocuments<TData = void>(id: string,
+    provideDocumentsRequest: ProvideDocumentsRequest, options?: HttpClientEventOptions): Observable<HttpEvent<TData>>;
+ postSelfServiceRegistrationsIdDocuments<TData = void>(id: string,
+    provideDocumentsRequest: ProvideDocumentsRequest, options?: HttpClientResponseOptions): Observable<AngularHttpResponse<TData>>;
   postSelfServiceRegistrationsIdDocuments<TData = void>(
-    id: string, options?: HttpClientObserveOptions): Observable<TData | HttpEvent<TData> | AngularHttpResponse<TData>> {
+    id: string,
+    provideDocumentsRequest: ProvideDocumentsRequest, options?: HttpClientObserveOptions): Observable<TData | HttpEvent<TData> | AngularHttpResponse<TData>> {
     if (options?.observe === 'events') {
       return this.http.post<TData>(
       `/self-service/registrations/${id}/documents`,
-      undefined,{
+      provideDocumentsRequest,{
         ...(options as Omit<NonNullable<typeof options>, 'observe'>),
         observe: 'events',
       }
@@ -244,7 +256,7 @@ export class BffApiV1Service {
     if (options?.observe === 'response') {
       return this.http.post<TData>(
       `/self-service/registrations/${id}/documents`,
-      undefined,{
+      provideDocumentsRequest,{
         ...(options as Omit<NonNullable<typeof options>, 'observe'>),
         observe: 'response',
       }
@@ -253,7 +265,7 @@ export class BffApiV1Service {
 
     return this.http.post<TData>(
       `/self-service/registrations/${id}/documents`,
-      undefined,{
+      provideDocumentsRequest,{
         ...(options as Omit<NonNullable<typeof options>, 'observe'>),
         observe: 'body',
       }
diff --git a/services/acl/Acl.Api/Program.cs b/services/acl/Acl.Api/Program.cs
index f220cb1..9581455 100644
--- a/services/acl/Acl.Api/Program.cs
+++ b/services/acl/Acl.Api/Program.cs
@@ -40,6 +40,15 @@ app.MapPost("/zaken/reference", async (ZaakReferenceRequest body, AclService acl
     return Results.Ok(new { reference });
 });
 
+// Store an uploaded diploma against a zaak (S-10b): the domain sends the file as base64; the ACL
+// creates the ZGW enkelvoudiginformatieobject and relates it to the zaak (§8.1). Returns its URL.
+app.MapPost("/documenten", async (StoreDocumentRequest body, AclService acl, CancellationToken ct) =>
+{
+    var url = await acl.StoreDiplomaAsync(
+        new Uri(body.ZaakUrl), Convert.FromBase64String(body.ContentBase64), body.FileName, body.ContentType, ct);
+    return Results.Ok(new { informatieobjectUrl = url.ToString() });
+});
+
 app.Run();
 
 public sealed record OpenZaakRequest(string Bsn, string Reference);
@@ -48,4 +57,6 @@ public sealed record SetStatusRequest(string ZaakUrl);
 
 public sealed record ZaakReferenceRequest(string ZaakUrl);
 
+public sealed record StoreDocumentRequest(string ZaakUrl, string ContentBase64, string FileName, string ContentType);
+
 public partial class Program;
diff --git a/services/acl/Acl.Application/AclDefaults.cs b/services/acl/Acl.Application/AclDefaults.cs
index 232d3a4..d378c8c 100644
--- a/services/acl/Acl.Application/AclDefaults.cs
+++ b/services/acl/Acl.Application/AclDefaults.cs
@@ -7,4 +7,8 @@ public sealed class AclDefaults
     public required string VerantwoordelijkeOrganisatie { get; init; }
     public required string Vertrouwelijkheidaanduiding { get; init; }
     public required Uri ZaaktypeUrl { get; init; }
+
+    /// <summary>The informatieobjecttype an uploaded diploma is filed under (S-10b). Seeded in the
+    /// catalogus and injected like <see cref="ZaaktypeUrl"/>.</summary>
+    public required Uri InformatieobjecttypeUrl { get; init; }
 }
diff --git a/services/acl/Acl.Application/AclService.cs b/services/acl/Acl.Application/AclService.cs
index a70e7ca..f692041 100644
--- a/services/acl/Acl.Application/AclService.cs
+++ b/services/acl/Acl.Application/AclService.cs
@@ -37,4 +37,33 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, ICloc
 
         return gateway.GetZaakIdentificatieAsync(zaakUrl, ct);
     }
+
+    /// <summary>
+    /// Store an uploaded diploma against the zaak (S-10b): default-fill the ZGW-mandatory document
+    /// fields (informatieobjecttype, bronorganisatie, vertrouwelijkheidaanduiding, taal, creatiedatum)
+    /// and hand the file to the gateway, which creates the informatieobject and relates it to the zaak.
+    /// The domain supplies only the zaak, the bytes, and the file's name/type (§8.1).
+    /// </summary>
+    public Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+        ArgumentNullException.ThrowIfNull(content);
+        ArgumentException.ThrowIfNullOrWhiteSpace(fileName);
+        ArgumentException.ThrowIfNullOrWhiteSpace(contentType);
+
+        var request = new DocumentRequest(
+            defaults.Bronorganisatie,
+            defaults.InformatieobjecttypeUrl,
+            defaults.Vertrouwelijkheidaanduiding,
+            zaakUrl,
+            clock.Today,
+            Titel: "Diploma",
+            Auteur: "zorgprofessional",
+            Taal: "nld",
+            Bestandsnaam: fileName,
+            Formaat: contentType,
+            Inhoud: content);
+
+        return gateway.StoreDocumentAsync(request, ct);
+    }
 }
diff --git a/services/acl/Acl.Application/DocumentRequest.cs b/services/acl/Acl.Application/DocumentRequest.cs
new file mode 100644
index 0000000..885148f
--- /dev/null
+++ b/services/acl/Acl.Application/DocumentRequest.cs
@@ -0,0 +1,17 @@
+namespace Acl.Application;
+
+/// <summary>The fully default-filled diploma document the gateway will create in the ZGW Documenten
+/// API and relate to the zaak (S-10b). <see cref="Inhoud"/> is the raw file content; the gateway
+/// base64-encodes it into the ZGW <c>inhoud</c> field.</summary>
+public sealed record DocumentRequest(
+    string Bronorganisatie,
+    Uri Informatieobjecttype,
+    string Vertrouwelijkheidaanduiding,
+    Uri Zaak,
+    DateOnly Creatiedatum,
+    string Titel,
+    string Auteur,
+    string Taal,
+    string Bestandsnaam,
+    string Formaat,
+    byte[] Inhoud);
diff --git a/services/acl/Acl.Application/IZaakGateway.cs b/services/acl/Acl.Application/IZaakGateway.cs
index 583baf5..73903f0 100644
--- a/services/acl/Acl.Application/IZaakGateway.cs
+++ b/services/acl/Acl.Application/IZaakGateway.cs
@@ -16,4 +16,11 @@ public interface IZaakGateway
     /// <summary>Read the zaak's <c>identificatie</c> — the public-safe reference the register shows.
     /// The Event Subscriber calls this through the ACL rather than reading ZGW itself (§8.1, #78).</summary>
     Task<string> GetZaakIdentificatieAsync(Uri zaakUrl, CancellationToken ct = default);
+
+    /// <summary>
+    /// Store a diploma document (S-10b): create an <c>enkelvoudiginformatieobject</c> in the ZGW
+    /// Documenten API and relate it to the zaak via a <c>zaakinformatieobject</c>. Returns the URL of
+    /// the created informatieobject.
+    /// </summary>
+    Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default);
 }
diff --git a/services/acl/Acl.Infrastructure/OpenZaakGateway.cs b/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
index 92d85ea..18907ab 100644
--- a/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
+++ b/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
@@ -80,6 +80,39 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         return zaak.Identificatie;
     }
 
+    public async Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        // 1. Create the enkelvoudiginformatieobject in the Documenten API (not a geo API — no CRS).
+        var created = await PostForUrlAsync(
+            "/documenten/api/v1/enkelvoudiginformatieobjecten",
+            new EnkelvoudigInformatieobjectDto(
+                request.Bronorganisatie,
+                request.Creatiedatum.ToString("yyyy-MM-dd"),
+                request.Titel,
+                request.Auteur,
+                request.Taal,
+                request.Informatieobjecttype.ToString(),
+                Convert.ToBase64String(request.Inhoud),
+                request.Bestandsnaam,
+                request.Inhoud.Length,
+                request.Vertrouwelijkheidaanduiding,
+                request.Formaat,
+                "definitief",
+                // No usage-rights restrictions apply. Left null, OpenZaak rejects closing the related
+                // zaak with "indicatiegebruiksrecht-unset"; false records the deliberate "none" answer.
+                false),
+            "Creating the informatieobject", ct);
+
+        // 2. Relate it to the zaak (Zaken API — no CRS).
+        await PostAsync("/zaken/api/v1/zaakinformatieobjecten",
+            new ZaakInformatieobjectDto(request.Zaak.ToString(), created.ToString()),
+            "Relating the informatieobject to the zaak", ct);
+
+        return created;
+    }
+
     // POSTs a non-geo ZGW resource (resultaat/status — no CRS headers). Buffers the body so uwsgi gets
     // a Content-Length instead of a chunked body (as with zaak-create).
     private async Task PostAsync(string path, object dto, string action, CancellationToken ct)
@@ -96,6 +129,26 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         await EnsureSuccessAsync(response, action, ct);
     }
 
+    // POSTs a non-geo ZGW resource and returns the created resource's URL (as PostAsync, but reads back
+    // the `url` of the created object). Buffers the body so uwsgi gets a Content-Length.
+    private async Task<Uri> PostForUrlAsync(string path, object dto, string action, CancellationToken ct)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Post, new Uri(options.BaseUrl, path))
+        {
+            Content = JsonContent.Create(dto),
+        };
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+        await message.Content.LoadIntoBufferAsync(ct);
+
+        using var response = await http.SendAsync(message, ct);
+        await EnsureSuccessAsync(response, action, ct);
+
+        var created = await response.Content.ReadFromJsonAsync<CreatedDto>(ct)
+            ?? throw new InvalidOperationException($"OpenZaak returned an empty response for {action}");
+        return new Uri(created.Url);
+    }
+
     // EnsureSuccessStatusCode discards the response body; ZGW returns a JSON problem detail on 400 that
     // is essential for diagnosing a rejected request, so surface it in the exception.
     private static async Task EnsureSuccessAsync(HttpResponseMessage response, string action, CancellationToken ct)
@@ -182,4 +235,26 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
 
     private sealed record ResultaattypeDto(
         [property: JsonPropertyName("url")] string Url);
+
+    private sealed record CreatedDto(
+        [property: JsonPropertyName("url")] string Url);
+
+    private sealed record EnkelvoudigInformatieobjectDto(
+        [property: JsonPropertyName("bronorganisatie")] string Bronorganisatie,
+        [property: JsonPropertyName("creatiedatum")] string Creatiedatum,
+        [property: JsonPropertyName("titel")] string Titel,
+        [property: JsonPropertyName("auteur")] string Auteur,
+        [property: JsonPropertyName("taal")] string Taal,
+        [property: JsonPropertyName("informatieobjecttype")] string Informatieobjecttype,
+        [property: JsonPropertyName("inhoud")] string Inhoud,
+        [property: JsonPropertyName("bestandsnaam")] string Bestandsnaam,
+        [property: JsonPropertyName("bestandsomvang")] int Bestandsomvang,
+        [property: JsonPropertyName("vertrouwelijkheidaanduiding")] string Vertrouwelijkheidaanduiding,
+        [property: JsonPropertyName("formaat")] string Formaat,
+        [property: JsonPropertyName("status")] string Status,
+        [property: JsonPropertyName("indicatieGebruiksrecht")] bool IndicatieGebruiksrecht);
+
+    private sealed record ZaakInformatieobjectDto(
+        [property: JsonPropertyName("zaak")] string Zaak,
+        [property: JsonPropertyName("informatieobject")] string Informatieobject);
 }
diff --git a/services/acl/Acl.IntegrationTests/OpenZaakFixture.cs b/services/acl/Acl.IntegrationTests/OpenZaakFixture.cs
index a743913..32dece6 100644
--- a/services/acl/Acl.IntegrationTests/OpenZaakFixture.cs
+++ b/services/acl/Acl.IntegrationTests/OpenZaakFixture.cs
@@ -77,6 +77,18 @@ public sealed class OpenZaakFixture : IDisposable
         return JsonDocument.Parse(json).RootElement.Clone();
     }
 
+    /// <summary>The URL of the published "Diploma" informatieobjecttype (S-10b), or null when the
+    /// stack has not been seeded with OZ_PUBLISH=1. `status=definitief` returns published types only.</summary>
+    public async Task<Uri?> FindPublishedDiplomaInformatieobjecttypeAsync(CancellationToken ct = default)
+    {
+        var query = new Uri(BaseUrl, "/catalogi/api/v1/informatieobjecttypen?status=definitief");
+        var page = await GetJsonAsync(query, ct);
+        foreach (var iot in page.GetProperty("results").EnumerateArray())
+            if (iot.TryGetProperty("omschrijving", out var o) && o.GetString() == "Diploma")
+                return new Uri(iot.GetProperty("url").GetString()!);
+        return null;
+    }
+
     /// <summary>The zaaktype's eindstatus (terminal statustype) URL — the one an approval sets.</summary>
     public async Task<Uri> FindEindstatustypeAsync(Uri zaaktypeUrl, CancellationToken ct = default)
     {
diff --git a/services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs b/services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs
index 9cdac3c..f9c4c13 100644
--- a/services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs
+++ b/services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs
@@ -74,4 +74,58 @@ public sealed class OpenZaakGatewayIntegrationTests(OpenZaakFixture stack)
         var eindstatustype = await stack.FindEindstatustypeAsync(zaaktype!);
         Assert.Equal(eindstatustype.ToString(), status.GetProperty("statustype").GetString());
     }
+
+    [Fact]
+    public async Task Storing_a_diploma_creates_a_real_informatieobject_related_to_the_zaak()
+    {
+        var zaaktype = await stack.FindPublishedBigZaaktypeAsync();
+        Assert.True(zaaktype is not null,
+            "No published BIG-REGISTRATIE zaaktype found — seed the stack with OZ_PUBLISH=1.");
+        var informatieobjecttype = await stack.FindPublishedDiplomaInformatieobjecttypeAsync();
+        Assert.True(informatieobjecttype is not null,
+            "No published Diploma informatieobjecttype found — seed the stack with OZ_PUBLISH=1.");
+
+        var gateway = new OpenZaakGateway(stack.Http, stack.Options);
+        var zaakUrl = await gateway.OpenZaakAsync(new ZaakRequest(
+            Bronorganisatie: "517439943",
+            VerantwoordelijkeOrganisatie: "517439943",
+            Vertrouwelijkheidaanduiding: "openbaar",
+            Zaaktype: zaaktype!,
+            Startdatum: DateOnly.FromDateTime(DateTime.UtcNow),
+            Identificatie: Guid.NewGuid().ToString()));
+
+        var content = System.Text.Encoding.UTF8.GetBytes("%PDF-1.4 synthetic diploma\n");
+        var documentUrl = await gateway.StoreDocumentAsync(new DocumentRequest(
+            Bronorganisatie: "517439943",
+            Informatieobjecttype: informatieobjecttype!,
+            Vertrouwelijkheidaanduiding: "openbaar",
+            Zaak: zaakUrl,
+            Creatiedatum: DateOnly.FromDateTime(DateTime.UtcNow),
+            Titel: "Diploma",
+            Auteur: "zorgprofessional",
+            Taal: "nld",
+            Bestandsnaam: "diploma.pdf",
+            Formaat: "application/pdf",
+            Inhoud: content));
+
+        // The gateway returns the canonical informatieobject URL...
+        Assert.StartsWith(
+            new Uri(stack.BaseUrl, "/documenten/api/v1/enkelvoudiginformatieobjecten/").ToString(),
+            documentUrl.ToString());
+
+        // ...the document is really persisted with the default-filled fields...
+        var doc = await stack.GetJsonAsync(documentUrl);
+        Assert.Equal("diploma.pdf", doc.GetProperty("bestandsnaam").GetString());
+        Assert.Equal(informatieobjecttype.ToString(), doc.GetProperty("informatieobjecttype").GetString());
+        Assert.Equal(content.Length, doc.GetProperty("bestandsomvang").GetInt32());
+        // indicatieGebruiksrecht is recorded as "no restrictions"; left null, OpenZaak would refuse to
+        // close the zaak this document is related to (the S-10b regression that broke the e2e flow).
+        Assert.False(doc.GetProperty("indicatieGebruiksrecht").GetBoolean());
+
+        // ...and it is related to the zaak (a zaakinformatieobject links the two).
+        var relations = await stack.GetJsonAsync(new Uri(stack.BaseUrl,
+            "/zaken/api/v1/zaakinformatieobjecten?informatieobject=" + Uri.EscapeDataString(documentUrl.ToString())));
+        Assert.Contains(relations.EnumerateArray(),
+            r => r.GetProperty("zaak").GetString() == zaakUrl.ToString());
+    }
 }
diff --git a/services/acl/Acl.Tests/AclServiceTests.cs b/services/acl/Acl.Tests/AclServiceTests.cs
index 2e74c8f..fe2a81a 100644
--- a/services/acl/Acl.Tests/AclServiceTests.cs
+++ b/services/acl/Acl.Tests/AclServiceTests.cs
@@ -30,6 +30,15 @@ public class AclServiceTests
             ReadReferenceFor = zaakUrl;
             return Task.FromResult("REG-FROM-ZAAK");
         }
+
+        public DocumentRequest? StoredDocument;
+        public Uri DocumentResult { get; } = new("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/doc-1");
+
+        public Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default)
+        {
+            StoredDocument = request;
+            return Task.FromResult(DocumentResult);
+        }
     }
 
     private static AclDefaults Defaults() => new()
@@ -38,6 +47,7 @@ public class AclServiceTests
         VerantwoordelijkeOrganisatie = "517439943",
         Vertrouwelijkheidaanduiding = "openbaar",
         ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+        InformatieobjecttypeUrl = new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
     };
 
     private sealed class FixedClock(DateOnly today) : IClock
@@ -55,6 +65,7 @@ public class AclServiceTests
             VerantwoordelijkeOrganisatie = "517439943",
             Vertrouwelijkheidaanduiding = "openbaar",
             ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+            InformatieobjecttypeUrl = new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
         };
         var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
 
@@ -81,6 +92,7 @@ public class AclServiceTests
             VerantwoordelijkeOrganisatie = "517439943",
             Vertrouwelijkheidaanduiding = "openbaar",
             ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+            InformatieobjecttypeUrl = new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
         };
         var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
 
@@ -114,6 +126,41 @@ public class AclServiceTests
         Assert.Null(gateway.Approved);
     }
 
+    [Fact]
+    public async Task Storing_a_diploma_default_fills_the_document_fields_and_returns_its_url()
+    {
+        var gateway = new FakeGateway();
+        var defaults = Defaults();
+        var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
+        var zaak = new Uri("http://openzaak/zaken/api/v1/zaken/abc");
+
+        var url = await service.StoreDiplomaAsync(zaak, [1, 2, 3], "diploma.pdf", "application/pdf");
+
+        Assert.Equal(gateway.DocumentResult, url);
+        var req = gateway.StoredDocument!;
+        Assert.Equal(zaak, req.Zaak);
+        Assert.Equal(defaults.InformatieobjecttypeUrl, req.Informatieobjecttype);
+        Assert.Equal("517439943", req.Bronorganisatie);
+        Assert.Equal("openbaar", req.Vertrouwelijkheidaanduiding);
+        Assert.Equal(new DateOnly(2026, 6, 4), req.Creatiedatum);
+        Assert.Equal("nld", req.Taal);
+        Assert.Equal("diploma.pdf", req.Bestandsnaam);
+        Assert.Equal("application/pdf", req.Formaat);
+        Assert.Equal(new byte[] { 1, 2, 3 }, req.Inhoud);
+    }
+
+    [Fact]
+    public async Task Storing_a_diploma_rejects_null_or_blank_arguments()
+    {
+        var service = new AclService(new FakeGateway(), Defaults(), new FixedClock(new DateOnly(2026, 6, 4)));
+        var zaak = new Uri("http://openzaak/zaken/api/v1/zaken/abc");
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() => service.StoreDiplomaAsync(null!, [1], "d.pdf", "application/pdf"));
+        await Assert.ThrowsAsync<ArgumentNullException>(() => service.StoreDiplomaAsync(zaak, null!, "d.pdf", "application/pdf"));
+        await Assert.ThrowsAnyAsync<ArgumentException>(() => service.StoreDiplomaAsync(zaak, [1], " ", "application/pdf"));
+        await Assert.ThrowsAnyAsync<ArgumentException>(() => service.StoreDiplomaAsync(zaak, [1], "d.pdf", " "));
+    }
+
     [Fact]
     public async Task Reading_a_zaak_reference_returns_the_zaaks_identificatie()
     {
diff --git a/services/acl/Acl.Tests/OpenZaakGatewayTests.cs b/services/acl/Acl.Tests/OpenZaakGatewayTests.cs
index af568c8..e58c050 100644
--- a/services/acl/Acl.Tests/OpenZaakGatewayTests.cs
+++ b/services/acl/Acl.Tests/OpenZaakGatewayTests.cs
@@ -432,4 +432,114 @@ public class OpenZaakGatewayTests
         b64 = (b64.Length % 4) switch { 2 => b64 + "==", 3 => b64 + "=", _ => b64 };
         return Encoding.UTF8.GetString(Convert.FromBase64String(b64));
     }
+
+    // --- StoreDocumentAsync (diploma upload / S-10b) ---
+
+    private static readonly Uri Informatieobjecttype =
+        new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip");
+
+    private static DocumentRequest SampleDocument(byte[]? inhoud = null) => new(
+        Bronorganisatie: "517439943",
+        Informatieobjecttype: Informatieobjecttype,
+        Vertrouwelijkheidaanduiding: "openbaar",
+        Zaak: new Uri(ZaakUrl),
+        Creatiedatum: new DateOnly(2026, 6, 4),
+        Titel: "Diploma",
+        Auteur: "zorgprofessional",
+        Taal: "nld",
+        Bestandsnaam: "diploma.pdf",
+        Formaat: "application/pdf",
+        Inhoud: inhoud ?? [1, 2, 3, 4]);
+
+    // Routes the two document calls: POST /enkelvoudiginformatieobjecten (documenten) then
+    // POST /zaakinformatieobjecten (zaken).
+    private static StubHandler DocumentStub(Recorder rec) => new(async req =>
+    {
+        rec.Requests.Add(req);
+        rec.ContentLengths.Add(req.Content?.Headers.ContentLength);
+        rec.Bodies.Add(req.Content is null ? null : await req.Content.ReadAsStringAsync());
+
+        return req.RequestUri!.ToString().Contains("/enkelvoudiginformatieobjecten")
+            ? Json(HttpStatusCode.Created, """{"url":"http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/doc-1"}""")
+            : Json(HttpStatusCode.Created, """{"url":"http://openzaak/zaken/api/v1/zaakinformatieobjecten/rel-1"}""");
+    });
+
+    [Fact]
+    public async Task Storing_a_document_creates_the_informatieobject_then_relates_it_to_the_zaak()
+    {
+        var rec = new Recorder();
+
+        var url = await Gateway(DocumentStub(rec)).StoreDocumentAsync(SampleDocument([10, 20, 30]));
+
+        Assert.Equal("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/doc-1", url.ToString());
+
+        // 1. Create the enkelvoudiginformatieobject in the Documenten API.
+        var create = rec.Sent("/enkelvoudiginformatieobjecten");
+        Assert.Equal(HttpMethod.Post, create.Request.Method);
+        Assert.Equal("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten",
+            create.Request.RequestUri!.ToString());
+        Assert.Equal("Bearer", create.Request.Headers.Authorization!.Scheme);
+        Assert.Contains("\"bronorganisatie\":\"517439943\"", create.Body);
+        Assert.Contains("\"informatieobjecttype\":\"http://openzaak/catalogi/api/v1/informatieobjecttypen/dip\"", create.Body);
+        Assert.Contains("\"creatiedatum\":\"2026-06-04\"", create.Body);
+        Assert.Contains("\"titel\":\"Diploma\"", create.Body);
+        Assert.Contains("\"auteur\":\"zorgprofessional\"", create.Body);
+        Assert.Contains("\"taal\":\"nld\"", create.Body);
+        Assert.Contains("\"bestandsnaam\":\"diploma.pdf\"", create.Body);
+        Assert.Contains("\"formaat\":\"application/pdf\"", create.Body);
+        Assert.Contains("\"vertrouwelijkheidaanduiding\":\"openbaar\"", create.Body);
+        Assert.Contains("\"status\":\"definitief\"", create.Body);
+        // indicatieGebruiksrecht must be set explicitly (false = no usage restrictions); left null,
+        // OpenZaak refuses to close the zaak this document is related to ("indicatiegebruiksrecht-unset").
+        Assert.Contains("\"indicatieGebruiksrecht\":false", create.Body);
+        // The file content is base64-encoded into `inhoud`, with its byte length in `bestandsomvang`.
+        Assert.Contains($"\"inhoud\":\"{Convert.ToBase64String([10, 20, 30])}\"", create.Body);
+        Assert.Contains("\"bestandsomvang\":3", create.Body);
+
+        // 2. Relate that informatieobject to the zaak (Zaken API — no CRS).
+        var relate = rec.Sent("/zaakinformatieobjecten");
+        Assert.Equal(HttpMethod.Post, relate.Request.Method);
+        Assert.Equal("http://openzaak/zaken/api/v1/zaakinformatieobjecten",
+            relate.Request.RequestUri!.ToString());
+        Assert.Contains($"\"zaak\":\"{ZaakUrl}\"", relate.Body);
+        Assert.Contains("\"informatieobject\":\"http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/doc-1\"", relate.Body);
+    }
+
+    [Fact]
+    public async Task Storing_a_document_buffers_the_body_and_sends_no_crs_headers()
+    {
+        // uwsgi rejects a chunked body (Content-Length must be present); the Documenten API is not a
+        // geo API, so no CRS headers (unlike the Zaken zaak-create).
+        var rec = new Recorder();
+
+        await Gateway(DocumentStub(rec)).StoreDocumentAsync(SampleDocument());
+
+        var create = rec.Sent("/enkelvoudiginformatieobjecten");
+        Assert.NotNull(create.Length);
+        Assert.True(create.Length > 0);
+        Assert.False(create.Request.Headers.Contains("Accept-Crs"));
+        Assert.False(create.Request.Content!.Headers.Contains("Content-Crs"));
+    }
+
+    [Fact]
+    public async Task Storing_a_document_surfaces_an_openzaak_rejection()
+    {
+        var handler = new StubHandler(_ =>
+            Task.FromResult(new HttpResponseMessage(HttpStatusCode.BadRequest)
+            {
+                Content = new StringContent("""{"detail":"bad"}""", Encoding.UTF8, "application/json"),
+            }));
+
+        var ex = await Assert.ThrowsAsync<HttpRequestException>(
+            () => Gateway(handler).StoreDocumentAsync(SampleDocument()));
+        Assert.Contains("bad", ex.Message);
+    }
+
+    [Fact]
+    public async Task Storing_a_document_rejects_a_null_request()
+    {
+        var handler = new StubHandler(_ => throw new InvalidOperationException("should not be sent"));
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() => Gateway(handler).StoreDocumentAsync(null!));
+    }
 }
diff --git a/services/bff/Bff.Api/DownstreamClients.cs b/services/bff/Bff.Api/DownstreamClients.cs
index f935247..cf0e448 100644
--- a/services/bff/Bff.Api/DownstreamClients.cs
+++ b/services/bff/Bff.Api/DownstreamClients.cs
@@ -27,10 +27,11 @@ public interface IDomainClient
     /// unknown or not the caller's (404), so the BFF can relay a 404 rather than a 500.</summary>
     Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default);
 
-    /// <summary>Provide the documents the caller's own registration is waiting for ("documenten
-    /// aanleveren"). Owner-scoped by <paramref name="bsn"/>. Returns <c>false</c> when the domain
-    /// reports the registration is unknown or not the caller's (404), so the BFF can relay a 404.</summary>
-    Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default);
+    /// <summary>Provide (upload) the diploma the caller's own registration is waiting for ("documenten
+    /// aanleveren"). The file is carried base64-encoded. Owner-scoped by <paramref name="bsn"/>. Returns
+    /// <c>false</c> when the domain reports the registration is unknown or not the caller's (404).</summary>
+    Task<bool> ProvideDocumentsAsync(
+        string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default);
 
     /// <summary>The behandelaar's werkbak — registrations awaiting beoordeling.</summary>
     Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default);
@@ -68,10 +69,12 @@ public sealed class DomainClient(HttpClient http) : IDomainClient
         return true;
     }
 
-    public async Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default)
+    public async Task<bool> ProvideDocumentsAsync(
+        string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default)
     {
         using var response = await http.PostAsJsonAsync(
-            $"registrations/{registrationId}/documents", new { bsn }, ct);
+            $"registrations/{registrationId}/documents",
+            new { bsn, contentBase64, fileName, contentType }, ct);
         // The domain 404s an unknown or not-owned registration; relay that rather than fail hard.
         if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
             return false;
diff --git a/services/bff/Bff.Api/Program.cs b/services/bff/Bff.Api/Program.cs
index 940d5f2..f2a660a 100644
--- a/services/bff/Bff.Api/Program.cs
+++ b/services/bff/Bff.Api/Program.cs
@@ -109,13 +109,15 @@ app.MapPost("/self-service/registrations/{id}/withdraw", async (string id, Claim
 // forwarded to the domain, which owner-scopes the action and completes the WachtOpDocumenten task; a
 // registration that is unknown or not the caller's comes back 404. The real file upload + ZGW storage
 // is S-10b — this is the trigger that unblocks the process.
-app.MapPost("/self-service/registrations/{id}/documents", async (string id, ClaimsPrincipal user, IDomainClient domain, CancellationToken ct) =>
+app.MapPost("/self-service/registrations/{id}/documents", async (string id, ProvideDocumentsRequest body, ClaimsPrincipal user, IDomainClient domain, CancellationToken ct) =>
 {
     var bsn = user.FindFirstValue("bsn");
     if (string.IsNullOrWhiteSpace(bsn))
         return Results.BadRequest("The token carries no bsn claim.");
+    if (string.IsNullOrWhiteSpace(body?.ContentBase64))
+        return Results.BadRequest("A document is required.");
 
-    var provided = await domain.ProvideDocumentsAsync(id, bsn, ct);
+    var provided = await domain.ProvideDocumentsAsync(id, bsn, body.ContentBase64, body.FileName, body.ContentType, ct);
     return provided ? Results.NoContent() : Results.NotFound();
 })
     .RequireAuthorization()
@@ -163,6 +165,10 @@ app.Run();
 /// <summary>The behandelaar's decision on a registration.</summary>
 public sealed record DecideRequest(string Besluit);
 
+/// <summary>A diploma upload from the self-service portal — the file base64-encoded client-side, with
+/// its name and MIME type. The bsn is taken from the DigiD token, not this body.</summary>
+public sealed record ProvideDocumentsRequest(string ContentBase64, string? FileName = null, string? ContentType = null);
+
 // Behandel (medewerker-realm) authentication + authorization wiring (ADR-0013).
 internal static class BehandelAuth
 {
diff --git a/services/bff/Bff.Tests/BffFactory.cs b/services/bff/Bff.Tests/BffFactory.cs
index 492ab05..e1b5132 100644
--- a/services/bff/Bff.Tests/BffFactory.cs
+++ b/services/bff/Bff.Tests/BffFactory.cs
@@ -94,15 +94,15 @@ internal sealed class FakeDomainClient : IDomainClient
         return Task.FromResult(WithdrawSucceeds);
     }
 
-    public (string RegistrationId, string Bsn)? DocumentsProvidedFor { get; private set; }
+    public (string RegistrationId, string Bsn, string ContentBase64, string? FileName, string? ContentType)? DocumentsProvidedFor { get; private set; }
 
     /// <summary>Whether the fake domain reports the provide-documents as done (true → 204) or
     /// not-found/not-owned (false → 404). Tests set this to exercise the relay.</summary>
     public bool ProvideDocumentsSucceeds { get; set; } = true;
 
-    public Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default)
+    public Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default)
     {
-        DocumentsProvidedFor = (registrationId, bsn);
+        DocumentsProvidedFor = (registrationId, bsn, contentBase64, fileName, contentType);
         return Task.FromResult(ProvideDocumentsSucceeds);
     }
 
diff --git a/services/bff/Bff.Tests/SelfServiceEndpointTests.cs b/services/bff/Bff.Tests/SelfServiceEndpointTests.cs
index c8e0ccd..3b23b7b 100644
--- a/services/bff/Bff.Tests/SelfServiceEndpointTests.cs
+++ b/services/bff/Bff.Tests/SelfServiceEndpointTests.cs
@@ -114,7 +114,17 @@ public class SelfServiceEndpointTests
 
     private static HttpRequestMessage ProvideDocuments(string? bearer, string id = "reg-123")
     {
-        var request = new HttpRequestMessage(HttpMethod.Post, $"/self-service/registrations/{id}/documents");
+        var request = new HttpRequestMessage(HttpMethod.Post, $"/self-service/registrations/{id}/documents")
+        {
+            // The portal base64-encodes the file client-side and posts it as JSON (S-10b); the bsn is
+            // never in the body — it comes from the DigiD token.
+            Content = JsonContent.Create(new
+            {
+                contentBase64 = Convert.ToBase64String([1, 2, 3]),
+                fileName = "diploma.pdf",
+                contentType = "application/pdf",
+            }),
+        };
         if (bearer is not null)
             request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
         return request;
@@ -132,14 +142,19 @@ public class SelfServiceEndpointTests
     }
 
     [Fact]
-    public async Task Provides_documents_for_the_callers_registration_forwarding_the_id_and_bsn()
+    public async Task Provides_documents_for_the_callers_registration_forwarding_id_bsn_and_file()
     {
         using var factory = new BffFactory();
 
         var response = await factory.CreateClient().SendAsync(ProvideDocuments(TestTokens.Valid("123456782"), "reg-9"));
 
         Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
-        Assert.Equal(("reg-9", "123456782"), factory.Domain.DocumentsProvidedFor);
+        var provided = factory.Domain.DocumentsProvidedFor;
+        Assert.NotNull(provided);
+        Assert.Equal("reg-9", provided!.Value.RegistrationId);
+        Assert.Equal("123456782", provided.Value.Bsn);
+        Assert.Equal(Convert.ToBase64String([1, 2, 3]), provided.Value.ContentBase64);
+        Assert.Equal("diploma.pdf", provided.Value.FileName);
     }
 
     [Fact]
diff --git a/services/bff/openapi.json b/services/bff/openapi.json
index fd2101a..02359e1 100644
--- a/services/bff/openapi.json
+++ b/services/bff/openapi.json
@@ -76,6 +76,16 @@
             }
           }
         ],
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/ProvideDocumentsRequest"
+              }
+            }
+          },
+          "required": true
+        },
         "responses": {
           "204": {
             "description": "No Content"
@@ -228,6 +238,29 @@
           }
         }
       },
+      "ProvideDocumentsRequest": {
+        "required": [
+          "contentBase64"
+        ],
+        "type": "object",
+        "properties": {
+          "contentBase64": {
+            "type": "string"
+          },
+          "fileName": {
+            "type": [
+              "null",
+              "string"
+            ]
+          },
+          "contentType": {
+            "type": [
+              "null",
+              "string"
+            ]
+          }
+        }
+      },
       "SubmitAccepted": {
         "required": [
           "registrationId",
diff --git a/services/domain/Big.Api/Program.cs b/services/domain/Big.Api/Program.cs
index c78e79b..56d6791 100644
--- a/services/domain/Big.Api/Program.cs
+++ b/services/domain/Big.Api/Program.cs
@@ -120,8 +120,17 @@ app.MapPost("/registrations/{id}/documents", async (string id, ProvideDocumentsR
 
     if (string.IsNullOrWhiteSpace(body?.Bsn))
         return Results.BadRequest(new { error = "A bsn is required to provide documents." });
+    if (string.IsNullOrWhiteSpace(body.ContentBase64))
+        return Results.BadRequest(new { error = "A document is required." });
 
-    var outcome = await provide.HandleAsync(new ProvideDocumentsCommand(new RegistrationId(guid), body.Bsn), ct);
+    byte[] content;
+    try { content = Convert.FromBase64String(body.ContentBase64); }
+    catch (FormatException) { return Results.BadRequest(new { error = "The document content is not valid base64." }); }
+
+    var command = new ProvideDocumentsCommand(
+        new RegistrationId(guid), body.Bsn, content,
+        body.FileName ?? "diploma.pdf", body.ContentType ?? "application/pdf");
+    var outcome = await provide.HandleAsync(command, ct);
     return outcome == ProvideDocumentsOutcome.Accepted ? Results.NoContent() : Results.NotFound();
 });
 
@@ -152,7 +161,7 @@ public sealed record DecideRequest(string Besluit);
 
 public sealed record WithdrawRequest(string Bsn);
 
-public sealed record ProvideDocumentsRequest(string Bsn);
+public sealed record ProvideDocumentsRequest(string Bsn, string ContentBase64, string? FileName = null, string? ContentType = null);
 
 public sealed record RegistrationResponse(string RegistrationId, string Status, string? ZaakUrl);
 
diff --git a/services/domain/Big.Application/Ports.cs b/services/domain/Big.Application/Ports.cs
index af12888..9d2c5e7 100644
--- a/services/domain/Big.Application/Ports.cs
+++ b/services/domain/Big.Application/Ports.cs
@@ -52,6 +52,13 @@ public interface IAclClient
     /// the zaak's final status — which OpenZaak notifies over NRC; the domain never names statustypen.
     /// </summary>
     Task ApproveZaakAsync(Uri zaakUrl, CancellationToken ct = default);
+
+    /// <summary>
+    /// Store an uploaded diploma against the zaak (S-10b). The domain hands over the zaak, the raw file
+    /// bytes, and the file's name/type; the ACL creates the ZGW informatieobject and relates it to the
+    /// zaak (§8.1). Returns the stored document's URL.
+    /// </summary>
+    Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default);
 }
 
 /// <summary>
diff --git a/services/domain/Big.Application/ProvideDocuments.cs b/services/domain/Big.Application/ProvideDocuments.cs
index c5cdcce..59d997f 100644
--- a/services/domain/Big.Application/ProvideDocuments.cs
+++ b/services/domain/Big.Application/ProvideDocuments.cs
@@ -2,10 +2,12 @@ using Big.Domain;
 
 namespace Big.Application;
 
-/// <summary>A zorgprofessional's signal that they have supplied the documents their registration is
-/// waiting for ("documenten aanleveren"). <paramref name="Bsn"/> is the authenticated caller (from the
-/// DigiD token, forwarded by the BFF): only the registration's own bsn may provide its documents.</summary>
-public sealed record ProvideDocumentsCommand(RegistrationId RegistrationId, string Bsn);
+/// <summary>A zorgprofessional's upload of the diploma their registration is waiting for ("documenten
+/// aanleveren"). <paramref name="Bsn"/> is the authenticated caller (from the DigiD token, forwarded by
+/// the BFF): only the registration's own bsn may provide its documents. <paramref name="Content"/> is
+/// the raw file, with its <paramref name="FileName"/> and <paramref name="ContentType"/>.</summary>
+public sealed record ProvideDocumentsCommand(
+    RegistrationId RegistrationId, string Bsn, byte[] Content, string FileName, string ContentType);
 
 /// <summary>The outcome of a provide-documents request.</summary>
 public enum ProvideDocumentsOutcome
@@ -19,14 +21,14 @@ public enum ProvideDocumentsOutcome
 }
 
 /// <summary>
-/// The provide-documents use case (S-10a): a zorgprofessional supplies the documents their registration
-/// is parked waiting for, completing the WachtOpDocumenten task so the registratie process leaves the
-/// 30-day wait and continues to beoordeling (ADR-0017). Owner-scoped by bsn. Completing the wait is
-/// best-effort: if the registration never started a process (or already left the wait), the request
-/// still stands, mirroring how <see cref="WithdrawRegistration"/> cancels best-effort. The actual file
-/// upload and its ZGW storage via the ACL is S-10b; this is the trigger that unblocks the process.
+/// The provide-documents use case (S-10a/S-10b): a zorgprofessional uploads the diploma their
+/// registration is parked waiting for. The document is stored in ZGW via the ACL (§8.1), then the
+/// WachtOpDocumenten task is completed so the registratie process leaves the 30-day wait and continues
+/// to beoordeling (ADR-0017). Owner-scoped by bsn. Both steps are best-effort about missing preconditions
+/// (mirroring <see cref="WithdrawRegistration"/>): storage needs an opened zaak, and completion needs a
+/// running process — a request that arrives before either still stands, storing/completing what it can.
 /// </summary>
-public sealed class ProvideDocuments(IRegistrationStore store, IWorkflowClient workflow)
+public sealed class ProvideDocuments(IRegistrationStore store, IWorkflowClient workflow, IAclClient acl)
 {
     public async Task<ProvideDocumentsOutcome> HandleAsync(ProvideDocumentsCommand command, CancellationToken ct = default)
     {
@@ -38,6 +40,11 @@ public sealed class ProvideDocuments(IRegistrationStore store, IWorkflowClient w
         if (registration is null || registration.Bsn != command.Bsn)
             return ProvideDocumentsOutcome.NotFound;
 
+        // Store the diploma against the zaak (once it is opened) — the ACL is the only ZGW caller (§8.1).
+        if (registration.ZaakUrl is not null)
+            await acl.StoreDiplomaAsync(
+                registration.ZaakUrl, command.Content, command.FileName, command.ContentType, ct);
+
         // Complete the document wait (if a process is running) so beoordeling can proceed.
         if (registration.ProcessInstanceId is not null)
             await workflow.CompleteDocumentWaitAsync(registration.ProcessInstanceId, ct);
diff --git a/services/domain/Big.Infrastructure/AclHttpClient.cs b/services/domain/Big.Infrastructure/AclHttpClient.cs
index 217f9dc..22c235c 100644
--- a/services/domain/Big.Infrastructure/AclHttpClient.cs
+++ b/services/domain/Big.Infrastructure/AclHttpClient.cs
@@ -31,6 +31,23 @@ public sealed class AclHttpClient(HttpClient http, AclOptions options) : IAclCli
         response.EnsureSuccessStatusCode();
     }
 
+    public async Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+        ArgumentNullException.ThrowIfNull(content);
+
+        // The file crosses this boundary base64-encoded in JSON — the domain and ACL contracts are
+        // JSON, and a diploma is small (S-10b, ADR). The ACL turns it into a ZGW informatieobject.
+        using var response = await http.PostAsJsonAsync(
+            new Uri(options.BaseUrl, "documenten"),
+            new StoreDocumentRequest(zaakUrl.ToString(), Convert.ToBase64String(content), fileName, contentType), ct);
+        response.EnsureSuccessStatusCode();
+
+        var stored = await response.Content.ReadFromJsonAsync<StoreDocumentResponse>(ct)
+            ?? throw new InvalidOperationException("The ACL returned an empty document response.");
+        return new Uri(stored.InformatieobjectUrl);
+    }
+
     private sealed record OpenZaakRequest(
         [property: JsonPropertyName("bsn")] string Bsn,
         [property: JsonPropertyName("reference")] string Reference);
@@ -38,4 +55,13 @@ public sealed class AclHttpClient(HttpClient http, AclOptions options) : IAclCli
     private sealed record OpenZaakResponse([property: JsonPropertyName("zaakUrl")] string ZaakUrl);
 
     private sealed record SetStatusRequest([property: JsonPropertyName("zaakUrl")] string ZaakUrl);
+
+    private sealed record StoreDocumentRequest(
+        [property: JsonPropertyName("zaakUrl")] string ZaakUrl,
+        [property: JsonPropertyName("contentBase64")] string ContentBase64,
+        [property: JsonPropertyName("fileName")] string FileName,
+        [property: JsonPropertyName("contentType")] string ContentType);
+
+    private sealed record StoreDocumentResponse(
+        [property: JsonPropertyName("informatieobjectUrl")] string InformatieobjectUrl);
 }
diff --git a/services/domain/Big.Tests/Fakes.cs b/services/domain/Big.Tests/Fakes.cs
index f183fda..ef539ef 100644
--- a/services/domain/Big.Tests/Fakes.cs
+++ b/services/domain/Big.Tests/Fakes.cs
@@ -110,4 +110,13 @@ internal sealed class FakeAclClient(Uri? zaakUrl = null) : IAclClient
         ApprovedZaakUrl = zaakUrl;
         return Task.CompletedTask;
     }
+
+    public (Uri ZaakUrl, byte[] Content, string FileName, string ContentType)? StoredDiploma { get; private set; }
+    public static readonly Uri DefaultDocumentUrl = new("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/doc");
+
+    public Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default)
+    {
+        StoredDiploma = (zaakUrl, content, fileName, contentType);
+        return Task.FromResult(DefaultDocumentUrl);
+    }
 }
diff --git a/services/domain/Big.Tests/ProvideDocumentsTests.cs b/services/domain/Big.Tests/ProvideDocumentsTests.cs
index 308d863..ed956e6 100644
--- a/services/domain/Big.Tests/ProvideDocumentsTests.cs
+++ b/services/domain/Big.Tests/ProvideDocumentsTests.cs
@@ -3,52 +3,60 @@ using Big.Domain;
 
 namespace Big.Tests;
 
-// S-10a (#102): the "documents received" use case. A zorgprofessional supplies the documents their
-// registration is waiting for; the handler completes the WachtOpDocumenten task via the Workflow Client
-// so the process leaves the 30-day wait and continues to beoordeling. Owner-scoped by the caller's bsn,
-// like WithdrawRegistration. (The real file upload + ZGW storage is S-10b; this is the trigger path.)
+// S-10a/S-10b (#102/#103): the "documents received" use case. A zorgprofessional supplies the diploma
+// their registration is waiting for; the handler stores it in ZGW via the ACL and completes the
+// WachtOpDocumenten task via the Workflow Client so the process continues to beoordeling. Owner-scoped
+// by the caller's bsn, like WithdrawRegistration.
 public class ProvideDocumentsTests
 {
     private const string Bsn = "123456782";
+    private static readonly Uri Zaak = new("http://openzaak/zaken/api/v1/zaken/abc");
 
     private static Registration Submitted(string processInstanceId = "proc-1")
     {
         var registration = Registration.Submit(Bsn);
         registration.RecordProcessStarted(processInstanceId);
+        registration.AttachZaak(Zaak);
         return registration;
     }
 
-    private static ProvideDocumentsCommand Command(RegistrationId id, string bsn = Bsn) => new(id, bsn);
+    private static ProvideDocumentsCommand Command(RegistrationId id, string bsn = Bsn) =>
+        new(id, bsn, [1, 2, 3], "diploma.pdf", "application/pdf");
 
     [Fact]
-    public async Task Providing_documents_completes_the_document_wait()
+    public async Task Providing_documents_stores_the_diploma_and_completes_the_wait()
     {
         var store = new FakeRegistrationStore();
         var registration = Submitted("proc-42");
         store.Seed(registration);
         var workflow = new FakeWorkflowClient();
-        var handler = new ProvideDocuments(store, workflow);
+        var acl = new FakeAclClient();
+        var handler = new ProvideDocuments(store, workflow, acl);
 
         var outcome = await handler.HandleAsync(Command(registration.Id));
 
         Assert.Equal(ProvideDocumentsOutcome.Accepted, outcome);
+        // Stored against the registration's zaak, carrying the uploaded bytes + file metadata.
+        Assert.Equal((Zaak, new byte[] { 1, 2, 3 }, "diploma.pdf", "application/pdf"), acl.StoredDiploma);
+        // …and the wait is completed so beoordeling can proceed.
         Assert.Equal("proc-42", workflow.CompletedDocumentWaitFor);
     }
 
     [Fact]
     public async Task A_different_bsn_cannot_provide_documents()
     {
-        // Owner-scoping: only the registration's own bsn may supply its documents. Another bsn is told
-        // NotFound (existence not revealed) and the wait is not completed.
+        // Owner-scoping: another bsn is told NotFound; nothing is stored or completed.
         var store = new FakeRegistrationStore();
         var registration = Submitted();
         store.Seed(registration);
         var workflow = new FakeWorkflowClient();
-        var handler = new ProvideDocuments(store, workflow);
+        var acl = new FakeAclClient();
+        var handler = new ProvideDocuments(store, workflow, acl);
 
         var outcome = await handler.HandleAsync(Command(registration.Id, bsn: "999999990"));
 
         Assert.Equal(ProvideDocumentsOutcome.NotFound, outcome);
+        Assert.Null(acl.StoredDiploma);
         Assert.Null(workflow.CompletedDocumentWaitFor);
     }
 
@@ -56,30 +64,33 @@ public class ProvideDocumentsTests
     public async Task Providing_for_an_unknown_registration_is_not_found()
     {
         var store = new FakeRegistrationStore();
-        var handler = new ProvideDocuments(store, new FakeWorkflowClient());
+        var handler = new ProvideDocuments(store, new FakeWorkflowClient(), new FakeAclClient());
 
         Assert.Equal(ProvideDocumentsOutcome.NotFound, await handler.HandleAsync(Command(RegistrationId.New())));
     }
 
     [Fact]
-    public async Task Providing_before_a_process_started_is_accepted_without_calling_the_workflow()
+    public async Task Providing_before_a_zaak_is_opened_does_not_store_but_still_completes_the_wait()
     {
-        // No process yet → no wait task to complete; the request still stands (best-effort, mirroring
-        // WithdrawRegistration) and the Workflow Client is not called.
+        // No zaak yet → nothing to file the document against, but the request still stands (best-effort,
+        // mirroring WithdrawRegistration). The wait is completed if a process is running.
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit(Bsn); // no RecordProcessStarted
+        var registration = Registration.Submit(Bsn);
+        registration.RecordProcessStarted("proc-9"); // process started, but no zaak attached
         store.Seed(registration);
         var workflow = new FakeWorkflowClient();
-        var handler = new ProvideDocuments(store, workflow);
+        var acl = new FakeAclClient();
+        var handler = new ProvideDocuments(store, workflow, acl);
 
         var outcome = await handler.HandleAsync(Command(registration.Id));
 
         Assert.Equal(ProvideDocumentsOutcome.Accepted, outcome);
-        Assert.Null(workflow.CompletedDocumentWaitFor);
+        Assert.Null(acl.StoredDiploma);
+        Assert.Equal("proc-9", workflow.CompletedDocumentWaitFor);
     }
 
     [Fact]
     public async Task Rejects_a_null_command()
         => await Assert.ThrowsAsync<ArgumentNullException>(() =>
-            new ProvideDocuments(new FakeRegistrationStore(), new FakeWorkflowClient()).HandleAsync(null!));
+            new ProvideDocuments(new FakeRegistrationStore(), new FakeWorkflowClient(), new FakeAclClient()).HandleAsync(null!));
 }
diff --git a/tests/acceptance/Steps/EenZaakOpenenSteps.cs b/tests/acceptance/Steps/EenZaakOpenenSteps.cs
index 04780e1..6dd2fc4 100644
--- a/tests/acceptance/Steps/EenZaakOpenenSteps.cs
+++ b/tests/acceptance/Steps/EenZaakOpenenSteps.cs
@@ -30,6 +30,7 @@ public sealed class EenZaakOpenenSteps
             VerantwoordelijkeOrganisatie = values["verantwoordelijkeOrganisatie"],
             Vertrouwelijkheidaanduiding = values["vertrouwelijkheidaanduiding"],
             ZaaktypeUrl = new Uri(values["zaaktype"]),
+            InformatieobjecttypeUrl = new Uri("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
         };
     }
 
diff --git a/tests/acceptance/Support/BffAcceptanceHost.cs b/tests/acceptance/Support/BffAcceptanceHost.cs
index ee4cd8c..75f492f 100644
--- a/tests/acceptance/Support/BffAcceptanceHost.cs
+++ b/tests/acceptance/Support/BffAcceptanceHost.cs
@@ -72,7 +72,8 @@ public sealed class CapturingDomainClient : IDomainClient
     public Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default)
         => Task.FromResult(true);
 
-    public Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default)
+    public Task<bool> ProvideDocumentsAsync(
+        string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default)
         => Task.FromResult(true);
 
     public Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
diff --git a/tests/acceptance/Support/InMemoryDomainPorts.cs b/tests/acceptance/Support/InMemoryDomainPorts.cs
index f480320..c63b05e 100644
--- a/tests/acceptance/Support/InMemoryDomainPorts.cs
+++ b/tests/acceptance/Support/InMemoryDomainPorts.cs
@@ -59,6 +59,14 @@ public sealed class InMemoryAclClient : IAclClient
         ApprovedZaakUrl = zaakUrl;
         return Task.CompletedTask;
     }
+
+    public (Uri ZaakUrl, string FileName)? StoredDiploma { get; private set; }
+
+    public Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default)
+    {
+        StoredDiploma = (zaakUrl, fileName);
+        return Task.FromResult(new Uri("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/acc-doc"));
+    }
 }
 
 /// <summary>An in-memory user-task client for the beoordeling acceptance scenario: it holds one open
diff --git a/tests/acceptance/Support/InMemoryZaakGateway.cs b/tests/acceptance/Support/InMemoryZaakGateway.cs
index 09c6414..e9e205d 100644
--- a/tests/acceptance/Support/InMemoryZaakGateway.cs
+++ b/tests/acceptance/Support/InMemoryZaakGateway.cs
@@ -27,4 +27,7 @@ public sealed class InMemoryZaakGateway : IZaakGateway
 
     public Task<string> GetZaakIdentificatieAsync(Uri zaakUrl, CancellationToken ct = default)
         => Task.FromResult("ACC-REF-1");
+
+    public Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default)
+        => Task.FromResult(new Uri("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/acc-doc"));
 }
diff --git a/tests/e2e/registration.spec.ts b/tests/e2e/registration.spec.ts
index b508352..8274ecb 100644
--- a/tests/e2e/registration.spec.ts
+++ b/tests/e2e/registration.spec.ts
@@ -56,6 +56,11 @@ test('DigiD submit → public INGEDIEND → documenten → behandelaar goedkeurt
   // why we supply the documents here rather than right after submit, when the trigger would race the
   // wait and no-op. (S-10b turns this into a real file upload; here it is the trigger that unblocks
   // beoordeling.)
+  await page.setInputFiles('#diploma', {
+    name: 'diploma.pdf',
+    mimeType: 'application/pdf',
+    buffer: Buffer.from('%PDF-1.4 synthetic diploma\n'),
+  });
   await page.getByRole('button', { name: /documenten aanleveren/i }).click();
   await expect(page.getByText(/documenten zijn aangeleverd/i)).toBeVisible();