[wallcraft]

For PDFs, you will get the actual page number. This is true on the Kindle's and the other devices.

For non-PDFs, e.g. AZW (MOBI) on the Kindle and ePubs on the others, you get a count of bytes into the file. The Kindle does this is 128 byte chunks of the uncompressed ebook, and Adobe Digital Editions (for ePub) does this essentially as 1024 byte chunks of the compressed ebook. So the ePub "pages" under ADE look like real pages (in length), but they are fake pages generated by a byte counting algorithm. The actual algorithm is complicated, each chapter starts a new page for example, but they are not real pages. The byte counts on the Kindle for AZW ebooks do not look like pages (because 128 bytes is too small), but it is a more reliable count of actual bytes.

If you are going to read lots of text-based PDFs, then the Kindle DX may be your best choice - because a big screen is much better for PDFs. On the KDX and on the K3, a PDF page is always shown "as is" and the zoom options are limited (which is more of an issue for the K3). On the others, you can either see the original page layout or the page can be "reflowed" to make the text bigger (but loosing the page layout). The page count is still accurate with reflow, and in fact the reflow is one page at a time.