People purposefully disallowing copy-paste isn't a problem with PDF: in other formats they would have embedded a picture, at least with PDF you get the other advantages of proper text: infinite zoom and great compression. Sadly there's also a lot of PDFs that are little more than a picture collection that looks like text, but that's hardly the file format's fault.

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)