Hack let you convert encrypted Mobipocket files that were intended for another reader so that that work on Kindle.
Amazon can do a lot of money only from selling kindle, like Apple does with the iPod.
Plenty of free e-books in Mobipocket format show up fine on Kindle.
There are converters available from Amazon and/or Mobi for pdf and doc files.
A revolutionary portable reader that wirelessly downloads books, newspapers, magazines and blogs to a crisp, high-resolution electronic paper display that looks and reads like real paper, even in bright sunlight.