Kindle File Extension

By Spanner Spencer

Only DRM-free e-books can be sent to the Kindle as an email attachment.
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The Amazon Kindle is compatible with several types of electronic book (e-book), and makes use of the various file types depending on the circumstances. E-books purchased through Amazon make use of the company's proprietary format, which includes a digital rights management, or DRM, protection system. The Kindle doesn't always require you to use copyright protected material, however, and accepts other formats in a DRM-free state.


Amazon launched its proprietary e-book format, which uses the ".AZW" prefix, at the same time as the original Kindle device was released. The format uses its own form of DRM protection to avoid copyright theft. It allows for all forms of text formatting and includes provision for illustrations and cover images within the e-books. The success of the Kindle device has driven the AZW format to a dramatic increase in popularity. It is now supported by a host of different electronic reading software and hardware besides the Kindle.


The Mobipocket e-book format is denoted by the ".MOBI" prefix, which is interchangeable with the ".PRC" file type originally popularized by the range of Palm Pilot PDA devices. The Kindle's own proprietary format is based on the Mobipocket standard but differs in its copyright protection method. MOBI e-books allow for text formatting, a cover image and electronic bookmarks. One of the longest-running e-book formats, MOBI is one of the most popular and widely supported types of electronic book. The Kindle is unable to use DRM-protected MOBI files, though Amazon now owns the Mobipocket company.


The Kindle originally did not support Adobe's popular PDF document file type. Compatibility has since been added through a software update, though this compatibility is limited to simple versions of the open-standard document type. PDFs often contain complex graphics, pagination and Internet functionality that the Kindle is unable to resolve, though most text-based documents can be displayed with reasonable accuracy. Even the latest Kindle model still carries the caveat that PDF support is experimental and documents might not display correctly.


Plain text files -- denoted by the ".TXT" file type -- are fully supported by the Kindle and have the advantage of creating very small file sizes and almost universal support on computers and portable devices. The disadvantage of displaying e-books using the TXT format is the lack of text-formatting options and no support within the document for annotations, illustrations or interactive features. The Kindle is able to add its own bookmarks to TXT files, however, ensuring the files are still a usable and practical choice for e-books.