diff --git a/src/app/main.tsx b/src/app/main.tsx
index ef3196e..dcc6da4 100644
--- a/src/app/main.tsx
+++ b/src/app/main.tsx
@@ -1,7 +1,16 @@
 import { StrictMode } from "react";
 import { createRoot } from "react-dom/client";
+import * as pdfjs from "pdfjs-dist";
+// Vite resolves `?url` to a bundled asset URL the browser can fetch.
+import pdfWorkerUrl from "pdfjs-dist/build/pdf.worker.min.mjs?url";
+
 import { App } from "./App";
 
+// PDF.js needs a worker URL before any PDF is parsed. Set it once at app
+// bootstrap so both the source-layer ingest (extract.ts) and the viewer
+// adapter (PdfSpikeViewer) can open documents.
+pdfjs.GlobalWorkerOptions.workerSrc = pdfWorkerUrl;
+
 const container = document.getElementById("root");
 if (!container) throw new Error("#root not found");
 
diff --git a/src/vite-env.d.ts b/src/vite-env.d.ts
new file mode 100644
index 0000000..11f02fe
--- /dev/null
+++ b/src/vite-env.d.ts
@@ -0,0 +1 @@
+/// <reference types="vite/client" />