How is an Adobe EPUB eBook different from a PDF file?
An Adobe EPUB eBook is a file that is DRM-protected using Adobe DRM (Digital Rights Management). DRM allows publishers to protect eBooks from unlawful distribution and to set certain restrictions on content, such as limits on copying and printing. Where a PDF is a static snapshot of a page, the text in an EPUB file is reflowable. This means you can change the font, resize the text, or alter the size of your display, and the text will rewrap itself to fit the available viewing area.