Amazon Kindle > Information Source
DRM is not to prevent other files from being readable on the Kindle.
If you read some of the Kindle discussion groups, you'll see people complaining about "no backlighting", and then a few days/weeks later they will be lauding the fact that it has no backlighting.
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.
Use Mobipocket software to convert PDFs to that format so you can read them on Kindle.
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