The script was crashing due to incorrect str-byte concatenation.  See the snippet below.
```bash
$ python3 pdf2john.py ~/win/Downloads/8527273050231012021.pdf
Traceback (most recent call last):
  File "pdf2john.py", line 329, in <module>
    parser.parse()
  File "pdf2john.py", line 116, in parse
    gecos = self.parse_meta_data(trailer)
  File "pdf2john.py", line 173, in parse_meta_data
    xmp_metadata_object = self.get_pdf_object(object_id)
  File "pdf2john.py", line 223, in get_pdf_object
    print(">>", repr(object_id.decode()))
AttributeError: 'str' object has no attribute 'decode'
```