.txt and .pdf are the absolute wrong formats for e-books. .pdf formatting is usually broken for eReaders, and .txt has no formatting whatsoever. Also, you'll really only ever get those formats if you're pirating, which usually entails transcription errors.

I used to pirate all my books, but it got to the point where I realized paying $6 for the pleasure of a properly-formatted, error-free book was a better deal than pirating and ripping them.