Update app.py

app.py

@@ -389,6 +389,12 @@ async def process_file(file_path):
     return str(tmp_file_path)
 
 
+def check_file(f):
+    if f is None:
+        raise gr.Error("Please upload a PDF or image before parsing.")
+    return f
+
+
 if __name__ == '__main__':
     with gr.Blocks() as demo:
         with gr.Row():
@@ -532,6 +538,10 @@ if __name__ == '__main__':
             lambda f: gr.update(visible=False),
             inputs=output_file,
             outputs=output_file
+        ).then(
+            fn=check_file,
+            inputs=file,
+            outputs=file
         ).then(
             fn=doc_parser,
             inputs=[file, prompts, model_selector],