PDF is not very fine. Copy-paste from PDF very often results in complete rubbish, even when it is not deliberately prevented (which the format allows, and then you have to do OCR).
It really is a problem with PDF that it's too easy to get a file where copy and paste yields a different result than what's displayed. But this varies widely with the software used for creating the file (e.g. latex ligatures never work in copy-paste)
When people write text and data and tables on the computer then put it on a paper-like format to share that's when the problem happens.