Update app.py

app.py

@@ -2297,6 +2297,7 @@ def download_sb3(project_id):
 
 @app.route("/download_pdf/<project_id>", methods=["GET"])
 def download_pdf(project_id):
+    pdf_path = GEN_PROJECT_DIR / f"{project_id}.pdf"
     if not pdf_doc.exists():
         return jsonify({"error": "Scratch project file not found"}), 404