There are converters available from Amazon and/or Mobi for pdf and doc files.
DRM is not to prevent other files from being readable on the Kindle.
Plenty of free e-books in Mobipocket format show up fine on Kindle.
We've known for some time already that Amazon's AZW files are actually Mobi files, but Amazon didn't share Kindle's Mobi PID which would allow one to buy encrypted Mobi books for Kindle.
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.