Update app.py

app.py

@@ -346,7 +346,8 @@ def generate_certificate(certificate_model, first_name, last_name):
     rgba = im
     rgb = Image.new('RGB', im.size, (255, 255, 255))  # white background
     rgb.paste(rgba, mask=rgba.split()[3]) # 3 is the alpha channel
-    pdf = rgb.save("certificate.pdf", 'PDF', resolution=100.0)    
+    pdf_ = rgb.save("certificate.pdf", 'PDF', resolution=100.0)   
+    pdf = pdf_.filename
 
     return im, pdf