[eboyhan]

If you have not engaged the new pdf zoom facility, the kindle examines the maximum left right extents of the whole document, and then compresses or expands the left right extent of the whole document so it is "fitted" to the width of the kindle. Then starting at the top of the doc it flows from top to bottom breaking the doc up into page "images" that will fill the kindle screen.

You can control the left right stuff a bit, but you have no control over where the kindle decides to place the page/screen breaks -- at least that's what it does with pdf's I create.

For professionally created store-bought pdfs, it appears that it will fit the whole printed page as laid out in the pdf onto the kindle screen -- this will often lead to lots of extraneous left/right whitespace (and a corresponding shrinking of the font size to make it all fit), but at least every printed book page will correspond to a single kindle screen -- no matter how small that page ends up being on the kindle. You could try to edit these with Acrobat (or other tools), but these mostly have drm -- so your ability to edit them is restricted.

If you then invoke the kindle zoom facility, the kindle created page "images" are blown up by whatever % you chose (150, 200, 300) and you have to use panning left/right and up/down to see whole page. Hitting the "next page" button will take you to the next kindle created page "image" which continues to be blown up by the zoom %, and you will have to use panning to see all of that page ... and so on.

I'm not sure whether the kindle actually creates real "images" for each page, or whether it just adjusts the pdf to give the impression of an image -- I suspect the latter.

the kindle does some flowing of the doc when it is opened for the first time (as described above), but it will not reflow the doc once opened in response to a zoom request

I haven't looked at the source or anything, so what I'm describing here is my mental model which has worked well for me in dealing with the pdf's (many) that I have created for my KDX. I describe the kindle as examining the whole pdf at doc open, but it could be doing some of it on the fly as well -- save that once it has decided on a left/right layout, it maintains that throughout the doc.