The three major book readers -- Kindle, Nook and iPad -- all have bookstores that sell files that are incompatible with their competitors' devices. While this is a major benefit for the manufacturers of the devices and operators of their respective book stores, it can cause a major headache for end users. There are some workarounds for this problem.
MOBI: Kindle E-Book Format
Amazon's Kindle e-book reader uses the Mobipocket e-book format. This format, which is loosely based on the Hypertext Markup Language standard that Web pages use, has been around for a number of years since it was first released on the Palm Pilot PDA. MOBI files sold by the Kindle bookstore typically contain a form of copyright protection called Digital Rights Management, which makes it impossible to use the files on anything other than the intended device or account.
EPUB: iPad and Nook E-Book Format
Both the Apple iPad and Barnes and Noble Nook e-readers use the EPUB format. This format uses the Extensible Markup Language standard that drives many advanced Web applications and offers a great deal of formatting flexibility. Because the two companies use different kinds of DRM, iBooks files can't be read on a Nook e-reader.
PDF: Generic E-Book Format
All three devices support the ubiquitous Adobe Acrobat Portable Document Format. PDF files are popular in many industries but have one key drawback for e-reader devices: they store documents as a series of pages with a fixed size. This makes them hard to view on some e-readers, especially devices that have small screens. In contrast, the MOBI and EPUB formats store the data that makes up the book and allow it to be dynamically reformatted to look good on different devices with different screen sizes,
Using E-Books on Other Platforms
If you need to use multiple formats of e-books all at once, your best option is to get either an iPad or an Android tablet other than a Kindle or Nook tablet. IPads can access all three book formats through the iBooks app for Apple EPUB books, the free Amazon Kindle app for MOBI books and the free Barnes and Noble Nook app for Barnes and Noble-formatted EPUB books. Android tablets such as the Motorola Xoom, Samsung Galaxy Tab or Acer Iconia can run both Nook and Kindle apps, although they cannot read iBooks e-book files. If you have files without Digital Rights Management, you can convert them between formats with the free and open-source Calibre e-book converter.
- Dynamic Graphics Group/Dynamic Graphics Group/Getty Images