Originally Posted by rdg_lad
I am under the impression Kindle will only support those e-books which are purchased from Amazon.com. Is that true?
No, it's not true. The only thing restricted to Amazon is the DRM system.
Non-DRM books in any of the formats the Kindle supports (mobi, pdf, HTML, text, a few others, IIRC) can be read from any source, and most other non-DRMed formats can be easily converted to one of the supported formats by tools like Calibre.
content from other stores besides Amazon would require stripping the DRM first and then converting.
While the Kindle can read PDFs, I don't think I'd enjoy reading many PDFs on my Kindle.
For text based PDFs, I think the Sony readers probably offer the best experience, though I really don't think any current 6-inch eink reader is going to be that great for PDF, especially graphically-rich ones.