The attached PDF contains a fill-able form - maybe that's the 'catch'
Code:
calibre, version 2.56.0
WARNING: Failed for some files: Failed to embed metadata into some book files. Click "Show details" for details.
The PDF format of demo:
Traceback (most recent call last):
File "site-packages\calibre\customize\ui.py", line 392, in set_file_type_metadata
File "site-packages\calibre\customize\builtins.py", line 499, in set_metadata
File "site-packages\calibre\ebooks\metadata\pdf.py", line 158, in set_metadata
File "site-packages\calibre\utils\podofo\__init__.py", line 41, in set_metadata
Exception: Failed to set PDF metadata in (demo): Traceback (most recent call last):
File "site-packages\calibre\utils\ipc\simple_worker.py", line 274, in main
File "site-packages\calibre\utils\podofo\__init__.py", line 57, in set_metadata_
Error: A number was expected but not found.
BR