Update app.py

app.py

@@ -238,7 +238,7 @@ def generate_pdf_report(original_img: Image.Image, mask: np.ndarray, overlay: Im
         pdf.cell(text="This report was generated by DR Analysis System", new_x="LMARGIN", new_y="NEXT", align='C')
         
         # Get PDF as bytes - updated for fpdf2>=2.7.6
-        pdf_bytes = pdf.output()  # Returns bytes directly in newer versions
+        pdf_bytes = bytes(pdf.output()) # Returns bytes directly in newer versions
         return pdf_bytes
     
     except Exception as e: