(Clippage)..In a reflowed document, text remains at its original size even when the window size changes, so that it's easier to view. In contrast, images reduce in size to accommodate a smaller window size, so that they can be viewed at a glance....
Some readers do reflow, but even the ones that do may have issues with some pdf's. They have to be created correctly, "tagged" in order to do reflow.
(more clippage)....PDF is so widely used because it presents information in a uniform, fixed fashion. This means that whether you view PDF Document A on your computer, a friend's or (just about) anywhere else, the document will be pretty much exactly as it was meant to be viewed, thus ensuring reliable viewing and printing. There are caveats, of course, regarding embedded fonts and such, but it's an extremely reliable way to ensure documents are the way you want them to be when you send them out or make them available to others.
One of the biggest strengths of PDF -- its uniform, fixed formatting for easy viewing and printing -- is one of its biggest shortcomings in the e-reader world. However, you can create a tagged PDF file to resolve this issue. Tagged PDF files can be reflowed, such that when the tagged file is viewed on a reader device its text and images will reflow to fit on the smaller screen. If you are creating PDF documents for viewing on readers, you can create them as tagged PDF files and if the reader supports reflow, you will be able to view the documents in reflow mode......
That said, however, there are better formats for e-readers and the one I recommend is EPUB. EPUB is the industry standard for e-documents and e-books. Any e-reader that supports EPUB fully supports all of its advanced features, which includes advanced support for reflow, tables, figures and graphics. I'll write more about EPUB in upcoming posts, and as I am able.
If you have non-tagged or even tagged PDF files that you want to convert to EPUB, there are tools available that allow you to covert these PDF files to EPUB. Once you do this, you'll have a better viewing and reading experience on your e-reader.
The other option for most readers is zoom, which has the advantage in that the document doesn't change.
However you may have to scroll up down, left right for each page. Which very quickly becomes a very real pain.
In my experience, if a PDF is just text, it converts quite nicely with several different tools to a basic text file.
*.txt
The better tools will probably have the ability to save as *.rtf, or *.epub.
The only exception to this that I am aware of would be the Kindle DX.
Being large enough to display PDF's without having to reflow or zoom.
But I don't know if it can be loaded directly via computer & usb cable.
Or if it has to be emailed to kindle and "converted" and placed on your bookshelf.
Best chance for exact answers are going to be in the MobileRead Kindle section.