The (free) Windows MobiPocket Reader can import DRM-free PDFs and export (and display) them as MOBI ebooks. The Amazon conversion is thought to be very similar, but it may work in cases that Mobipocket's fail. Amazon owns MobiPocket, and the the Kindle essentially only reads MOBI ebooks (Amazon calls them AZWs, but they are MOBI).
The conversion works well in some cases, but is terrible in other cases.
There are other conversion options, including Calibre (has its own forum). However, version 6 of Calibre (due out soon) is supposed to have better PDF import than the existing version.
Another option is
PDFRead, which converts the original pages into images, typically multiple images per page. Use the prc-mobi or prc-mobi-p options and view them (for now) using Windows MobiPocket Reader.