I have noticed multiple times that okular has the option to “Speak Whole Document” and “Speak Current Page”, but it's not something I really use.

I tried it today, I had to install the package speech-dispatcher to make it work, and then it did.

However, you probably also need to install a text-to-speech program and it's speech-dispatcher output module, because at least under debian the default is to use espeak, which is... characteristic :D and I know of a few, but I don't know which ones would be considered reasonably decent to listen to.

Pros: okular opens everything
Cons: quite a bit of research and fiddling required to make it work in a *good* way