[any ANONYMOUS forum user]

All major ebook sellers use DRM (Digital Rights Management) protection:

• Amazon Kindle Store sells DRM protected .AZW ebooks. You can read them on your Kindle,
  Kindle and Kindle DX ebook readers, as well as using Kindle for PC, Kindle for iPhone, Kindle for iPad, Kindle for Mac, Kindle for Android, Kindle for Blackberry apps.
• Barnes and Noble. You can read them on a Nook reader or on your computer only.
• Apple iBookstore sells DRM protected ebooks that can be read on your iPad, iPhone, iPod Touch.

DRM protection prevents you from reading your legally purchase ebooks on any device you have. These books are technically licensed rather than purchased. Luckily you can remove DRM protection from:

• Kindle AZW files
• Adobe Digital Editions EPUB files
• Adobe Digital Editions PDF files