With Calibre you can put almost anything on your Kindle, which is nice.
If you have DRM encumbered files obviously you're going to need to do something else, first, but why did you buy a book with DRM? Seems unwise to begin with lol
Can you imagine buying a dead tree book and have the publisher come up and say "no no no, you can't sell that when you're done!"
DRM'd ebooks. What a world.