How is an EPUB eBook different from a PDF file?

Adobe EPUB eBooks offer reflowable text, which means that you can change the font, resize the text, or alter the size of your display and the text of the Adobe EPUB eBook 'reflows' to fill the available view area. This makes Adobe EPUB eBooks the optimal choice for reading eBooks on small screens. While some PDFs are reflowable on some devices (such as the Sony Reader), one of the main strengths of the PDF format is its ability to preserve the layout of complex documents.