If you want a preview of how "reflow" will work on your PDFs, download Sony Reader Library
for Windows or Mac. This uses a variant of the same mobile Adobe Digital Editions software as the EZ Readers. For a PDF, the "S" font size is the full page view and the other font sizes are reflowed versions of the document. Reflow is essentially extracting the text (and images) out of the PDF and displaying them with different font sizes. This will work if the text and images are placed in the PDF in a "simple" manner. As Robertb says, almost all EInk Reading devices do PDF reflow using the same (mobile ADE) software.