workflows: open generated pdf file in binary mode (#36515)

wcs/wf/export_to_model.py

@@ -75,7 +75,7 @@ try:
                 subprocess.check_call(['libreoffice', '--headless', '--convert-to', 'pdf',
                                        infile.name, '--outdir', temp_dir], stdout=dev_null,
                                       stderr=dev_null)
-            return open(infile.name + '.pdf')
+            return open(infile.name + '.pdf', 'rb')
         except subprocess.CalledProcessError:
             raise Exception('libreoffice is failing')
         finally: