Well, one version of the Kindle device had the ability to read text to you. And of course, many books have audio versions, too, and with Kindle, if you buy the text version of a book, you can get the audio version at a big discount. The idea is you can read sometimes, then listen sometimes, and switch up.
If all you have is a PDF in text format, then your only option so to try some text-to-speech apps or programs. I found one very quickly with a google search.