Kindles can read a variety of non-proprietary, non-DRM'ed formats. They read TXT, HTML, JPEG, and non-DRM Mobi files directly.
Hack let you convert encrypted Mobipocket files that were intended for another reader so that that work on Kindle.
The Kindle only allows the reading of Amazon DRM-protected content.
Use Mobipocket software to convert PDFs to that format so you can read them on 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.