A tablet could be useful if it's large enough, at least 10 inches. The Kindle Fire HD strikes me as too small, even the 8.9 inch version. Also, you may need to root it.
If I were you, I'd go with a Samsung, Acer, Asus, whichever has the largest screen for the money. The best Android software for reading pdf is EbookDroid, free on Google Play.
On the other hand, even a tablet will only give you small version of your computer screen, which is not ideal for reading because of the backlight. Personally, I've had mixed experiences with tablets. I'm waiting for screens that will use something like e-ink technology, only bigger and faster. Until then I'll stick to the desktop computer and printed material. Besides, I think that if a book is really worth reading, it's worth having in printed format. Computers are great tools, but so are printed books, post-its, and a pencil and paper.