? Yes it is, as long as you have the necessary hardware (flash card for DS, etc.) I don't have a PSP, but I'm pretty positive it's possible on one.
For the DS, I tend to just read txt files with Moonshell. ComicBookDS is great for manga or comics (have to convert it to their format first, doesn't take too long). I think there is some program that can read docs, but I don't recall what it is. FlipDS (
http://sourceforge.net/projects/flipds ) looks like it will be a promising final solution to all of this, but it hasn't been released at all yet. In any case, you can easily read txt files on the NDS with the proper hardware, and save your position in books, etc.