EPUB (short for electronic publication; alternatively capitalized as ePub, ePUB, EPub, or epub, with "EPUB" preferred by the vendor) is a free and open e-book standard by the International Digital Publishing Forum (IDPF). Files have the extension .epub.
EPUB is designed for reflowable content, meaning that the text display can be optimized for the particular display device used by the reader of the EPUB-formatted book. The format is meant to function as a single format that publishers and conversion houses can use in-house, as well as for distribution and sale.
How to convert DRM-protected ePub ebooks onto Apple iPad, iPhone, iPod Touch
The easiest way to remove Adobe Digital Editions DRM from ePub files is by using a
Calibre DRM removal plug-in. After removing DRM with Calibre, you can convert Kindle Store ebooks to many popular ebook formats including ePub/fb2/LRF/Mobi/PDF/PDB/TXT/RTF/LIT.
Download Calibre ePub DRM removal plug-in and standalone ePub DRM removal software:
ebook DRM removal tools archive
What software to use to read ePub ebooks on iPad/iPhone/iPod Touch