small bugfix

app.py

@@ -21,8 +21,8 @@ def pdf_to_document_store(pdf_files):
     converter = PDFToTextConverter(remove_numeric_tables=True, valid_languages=["en"])
     documents = []
     for pdf in pdf_files:
-        docs = converter.convert(file_path=pdf.name, meta=None)
-        documents.append(docs)
+        doc = converter.convert(file_path=pdf.name, meta=None)[0]
+        documents.append(doc)
     preprocessed_docs = preprocessor.process(documents)
     document_store.write_documents(preprocessed_docs)
     return None