Most Common eBook Formats
This list comprises of the most common ebook formats used by ebook readers and ebook reader software. For information about converting format file types, click on the ebook software page.
AZW: Amazon's proprietary format; similar to MOBI. With this format, DRM protected files cannot be viewed by other devices. If it's an unprotected file, such as personal documents converted to AZW, the file extension can be changed to .prc and .mobi to view with different devices.
BBEB: Sony's proprietary format; stands for Broadband eBook. There are three file type variants: .lrx for DRM protected; .lrf for non-encrypted; and .msd for dictionaries.
CHM: Stands for compressed HTML. Used for large reference manuals and help documentation. Windows uses CHM for help files.
DJVU: A format by Lizardtech; widely used for scientific publications. DJVU uses advanced compression techniques for high-resolution images of scanned documents, digital documents, and photographs. Its compression ratio is about 10x better than PDF, and retains the same high quality.
DOC: Not to be confused with PalmDOC, .doc is Microsoft word's format. Can be converted to other file types for improved ebook viewing.
EPUB: A popular open ebook standard defined by the International Digital Publishing Forum (IDPF). EPUB is based on XHTML and XML and is one of the more popular ebook formats. Adobe Digital Editions uses EPUB formatting.
FB2: Stands for Fiction Book version 2; based on XML. FB2's main focus is to preserve accurate ebook structure and to make it easy to convert to other popular ebook formats.
HTML: Stands for HyperText Markup Language; the language used by all internet websites that any browser can read.
LIT: The native format used for Microsoft Reader.
LRF: Sony's proprietary format. See BBEB.
MOBI: A widely used, very popular format by Mobipocket; also can be .prc. Mobipocket's software can convert .chm, .doc, .html, .ocf, .pdf, .rtf, and .txt files to this format.
PDB: Stands for palm database. This format is widely used for cellphones (BlackBerry, iPhone), and Palm devices. Plucker, PalmDOC, iSilo, eReader, zTXT, and many more.
PDF: Stands for Portable Document Format. The most widely used file type. Created by Adobe. Most ebook readers support PDF, but it's a challenge to display a 14" diagonal page on a 6" diagonal screen. There are conversion softwares, such as Calibre, that reformat PDF to display better on ebook readers.
PRC: Stands for Palm Resource Compiler; aka MOBI.
RTF: Stands for Rich Texture Format; one of the most widely interchangeable ebook formats and supported by most ebook readers and word processors. RTF retains special characters and text formatting.
TXT: Plain text files don't retain special characters or formatting; basic notepad style.
WOLF: The proprietary format for Hanlin ebook readers, aka BeBook; extension .wol.
What is DRM?
If you are considering buying a Kindle, Sony Reader, or other type of ebook reader, you may be wondering what non-DRM and DRM supported files mean.
DRM stands for Digital Rights Management, but most believe a more apt definition would be Digital Restrictions Management, because DRM restricts consumers' access to all forms of purchased digital media, ebooks especially.
There are varying levels of DRM protection applied to ebooks. The restrictions may limit copying, printing, modifying, sharing, or even using a text-to-speech feature to read an ebook aloud. The specific levels of DRM are determined by publishers and distributors.
For example, if you own a Kindle and purchase a DRM protected ebook from their online store, you cannot transfer that ebook to your daughter's Sony Reader to read at school. You can, however, transfer that ebook to another Kindle under the same account, with up to six Kindles per account. You can't transfer DRM protected ebooks to read on other devices. Amazon does offer an application to read your ebook library with an iPhone and iPod touch, along with Kindle for PC.
Similar restrictions apply to other devices and ebookstores too in regard to registering a set number of devices. Most devices support Adobe DRM'ed EPUB and PDF. With these particular devices ebooks can be purchased and exchanged to read on other ebook readers more easily using Adobe Digital Editions.