diff --git a/src/source/pdf/viewer-url.test.ts b/src/source/pdf/viewer-url.test.ts
index 2e553ba..ce6b602 100644
--- a/src/source/pdf/viewer-url.test.ts
+++ b/src/source/pdf/viewer-url.test.ts
@@ -38,11 +38,16 @@ describe("resolvePdfViewerUrl", () => {
     );
   });
 
-  it("falls back to fixture path when only a stale blob uri is stored", () => {
+  it("returns null for stale blob uri without live bytes (no fixture guess)", () => {
     const store = createPdfByteStore();
     expect(
       resolvePdfViewerUrl(doc({ uri: "blob:revoked", title: "a.pdf" }), store),
-    ).toBe("/fixtures/pdfs/a.pdf");
+    ).toBeNull();
+  });
+
+  it("returns null when uri was stripped on persist and bytes are gone", () => {
+    const store = createPdfByteStore();
+    expect(resolvePdfViewerUrl(doc({ uri: undefined, title: "upload.pdf" }), store)).toBeNull();
   });
 });
 
@@ -51,4 +56,4 @@ describe("isEphemeralBlobUri", () => {
     expect(isEphemeralBlobUri("blob:http://localhost/x")).toBe(true);
     expect(isEphemeralBlobUri("/fixtures/pdfs/x.pdf")).toBe(false);
   });
-});
\ No newline at end of file
+});
diff --git a/src/source/pdf/viewer-url.ts b/src/source/pdf/viewer-url.ts
index 4768b0f..da36819 100644
--- a/src/source/pdf/viewer-url.ts
+++ b/src/source/pdf/viewer-url.ts
@@ -4,6 +4,10 @@
  * Uploaded PDFs are served via ephemeral `blob:` URLs owned by
  * `PdfByteStore`. Those URLs must not be persisted (see persistence
  * sanitization) and must be re-resolved from live bytes on every render.
+ *
+ * After a reload, bytes come back via IndexedDB hydrate into the byte store.
+ * Never invent a `/fixtures/pdfs/<title>` URL for arbitrary uploads — that
+ * path 404s (or returns HTML) and PDF.js reports "Invalid PDF structure".
  */
 
 import type { Document } from "@shared/document";
@@ -20,7 +24,8 @@ export function isEphemeralBlobUri(uri: string | undefined): boolean {
 
 /**
  * Prefer the byte store's live blob URL for uploaded documents; fall back
- * to a stable HTTP fixture path or a non-blob `document.uri`.
+ * to a stable non-blob `document.uri` (e.g. fixture HTTP path). Returns
+ * `null` when bytes are not available — ViewerShell shows re-upload copy.
  */
 export function resolvePdfViewerUrl(
   document: Document,
@@ -33,8 +38,8 @@ export function resolvePdfViewerUrl(
     return document.uri;
   }
 
-  const titleOrId = document.title ?? document.id;
-  return `/fixtures/pdfs/${encodeURIComponent(titleOrId)}`;
+  // Stale blob URI and no in-memory/IDB bytes: do not guess a fixture path.
+  return null;
 }
 
 /** True when bytes exist in the store but the document record lacks a URI. */
@@ -43,4 +48,4 @@ export function documentHasUploadedBytes(
   byteStore: PdfByteStore,
 ): boolean {
   return byteStore.has(documentId);
-}
\ No newline at end of file
+}
diff --git a/tests/integration/helpers/seed-session.ts b/tests/integration/helpers/seed-session.ts
index a7aa2e9..c2e8848 100644
--- a/tests/integration/helpers/seed-session.ts
+++ b/tests/integration/helpers/seed-session.ts
@@ -49,10 +49,18 @@ export function seedSessionWithDoc(opts: SeedOptions): SeedResult {
     lastOpenedAt: now,
   };
 
+  // Stable HTTP fixture URI so the viewer mounts without IndexedDB bytes.
+  // (resolvePdfViewerUrl no longer invents /fixtures paths from title alone —
+  // that produced "Invalid PDF structure" for arbitrary uploads after reload.)
   const document: Document = {
     id: documentId,
     mediaType: "application/pdf",
-    ...(opts.documentTitle ? { title: opts.documentTitle } : {}),
+    ...(opts.documentTitle
+      ? {
+          title: opts.documentTitle,
+          uri: `/fixtures/pdfs/${encodeURIComponent(opts.documentTitle)}`,
+        }
+      : {}),
     fingerprint: "seed-fingerprint",
     createdAt: now,
     updatedAt: now,