There can be issues with pdfs saving improperly and being corrupted, but the same thing can happen to a text file, or to literally any other file type.

Additionally, every modern web browser is capable of opening a pdf natively, so you don't even need a dedicated pdf reader. And if you have a computer without a web browser, then I'm curious how you're getting the books on it in the first place.

Lastly, even if you absolutely cannot open a PDF because a bandit has appeared behind you and threatened to shoot you if you open a pdf, there are still free ways to convert a pdf file to a .txt, so you could simply convert it into a text file and then read that if you absolutely needed to.

The only reason you'd run into problems with not being able to read a pdf is if you were technologically illiterate, but it would be much simpler for you to simply learn how to open a pdf than it would be for you to try to read an entire book in .txt format.