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/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/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"));
 }