So far as I can tell, the reflow capabilities of mobile Adobe Digital Editions has not changed over recent releases, so all devices from the PRS-505 to the Nook do reflow the same way. Reflow is on a page by page basis, so sometimes it is just one or a few pages that don't reflow.
One alternative is an off-line PDF to reflowable format conversion. The PDF has to be DRM-free first, but then Calibre is the obvious first choice to try.
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