Add underscore between lastname and firstname in file naming

pdf_renamer.py

@@ -429,7 +429,7 @@ def extract_names_from_pdf(pdf_path):
 
             if extracted_data and all(extracted_data.values()):
                 return {
-                    'filename': f"{extracted_data['last_name']}{extracted_data['first_name']}_{extracted_data['grade']}.pdf",
+                    'filename': f"{extracted_data['last_name']}_{extracted_data['first_name']}_{extracted_data['grade']}.pdf",
                     'last_name': extracted_data['last_name'],
                     'first_name': extracted_data['first_name'],
                     'grade': extracted_data['grade'],