Hello John,
You need to check, first of all, whether the extension of the file attached to the PDF is in your system MIME types. Does it have a specific format in attachments and links tab? If yes, is it docx or xlsx?Maintain Upper Limit for Size of Attachments
Check the size of the PDF files in the SPRO customizing -> Maintain Upper Limit for Size of Attachments. If it is 0, it does not have a specific limit.
Regards,
Fernando