Everything you need to know about e-books – part three: e-book formats

If you’re publishing a book in digital form, one of your main priorities will be to reach as many readers as possible. But whether or not a user can actually read the book easily on their device usually comes down to the file format you choose. This is an important issue, because the market for e-book readers is full of many different formats from a variety of manufacturers. And there’s no standard format for digital books that will be supported by all readers.

We’ve already looked at two important aspects of e-books in our series, beginning with how to create an e-book, before discussing the various e-book templates available for authors and publishers. Now, in the third part of our e-books series, we’ll take a look at the best and most popular e-book formats available on the market today, to help you decide which one is right for your needs.

Popular e-book formats

Modern e-book readers usually support a number of formats when it comes to displaying digital documents. While all of them prefer specifically designed standards for e-books that enable an optimized reading experience on portable devices, many also support current data formats that you’ll be familiar with from saving classic office documents. Choosing the right e-book format really comes down to two factors: the features required and the expected target platform. Here are a selection of the most popular and well-known e-book formats.


ePUB is a widely-used format when it comes to the publication of digital books. It was developed by the International Digital Publishing Forum (IDPF) and is supported by almost all e-book readers outside of the Amazon universe. This popular e-book format is based on standards like XHTML, XML, and CSS, and also supports HTML5, MathML, scalable vector graphics (SVG), and JavaScript embedding in version 3.

In addition to a stylish text formatting, this file format features integration of multimedia elements like images, audio files, and videos, as well as interactive elements. Digital books in ePUB format (.epub) are designed to fit dynamically to whatever display screen size the mobile device in question has. Alternatively, it’s possible to assign a fixed layout to content. For copyright protection, ePUB users have the option of an extension to Digital Rights Management (DRM), a system designed to handle copyright. Commercial ePUB e-books are protected by the Adobe software ADEPT DRM.

Amazon Kindle (MOBI, AZW, KF8)

While numerous e-book reader manufacturers remain flexible by making use of open standards, Amazon customers only have in-house formats available to use. Amazon e-book products are a closed system, consisting of the Kindle Shop, Kindle e-book readers, and the corresponding reader apps for computer, tablet, and smartphone. Amazon relies on its own file formats: Mobipocket, AWZ, and KF8, along with its own DRM system. This DRM system means that e-books purchased on Amazon can only be opened on Kindle devices or through Kindle apps.

  • Mobipocket: Mobipocket is an older e-book format from an Amazon subsidiary of the same name. Documents in Mobipocket format (.mobi) are supported by Kindle series reader devices and can be opened on older Windows versions (2000, XP, Vista) and mobile devices with the operating systems Palm OS, Symbian OS, or Windows Mobile via the Mobipocket e-book reader software. The e-book format is also supported by the free e-book viewer programs Okular and FBReader. Mobipocket is based on the same open e-book standard that serves as a template for ePUB, and likewise uses XHTML. But unfortunately, unlike other e-book formats, the Mobipocket format has rather restricted flexibility when it comes to layout. In the Amazon universe, Mobipocket formatting has been replaced by the continued development of AZW.
  • AZW: Technology-wise, the AZW format (.azw) is based on Mobipocket, but unlike its predecessor, AZW is exclusively supported by Amazon’s Kindle product range. E-books that are purchased in this format via the Kindle Shop can only be opened using Kindle devices or Amazon reader apps. Like Mobipocket, AZW has only limited layout options available. Amazon has since developed a new format with a much wider spectrum of functions and greater flexibility for the release of its Kindle Fire reading device series. Kindle Format 8 (KF8) is also compatible with other Kindle series devices.

Kindle Format 8 (KF8): The e-book format KF8 (.azw3) offers a marked increase in functions than the previous Amazon formats Mobipocket and AZW, largely thanks to the support of current web standards like HTML5 and CSS3. Documents in Kindle Format 8 adapt dynamically to the device’s screen size and enable complex graphic displays for design and layout dependent publications like children’s books and comics. Like ePUB, Kindle Format 8 supports the integration of audio and video as well as scalable vector graphics (SVG), fixed layouts, and interactive elements. But it’s not possible to use MathML or JavaScript with KF8. But users are able to integrate ePUB3 files into KF8 using an interface. The long-term plan is for this new e-book format to fully replace the traditional Mobipocket and AZW formats.


Like Amazon, Apple insists on its own e-book format: iBooks. But this management software for Mac, iPad, and iPhone also supports external file formats like ePUB or PDF. Digital documents can be created in iBook format through the iBooks Author software, which can be downloaded in the Mac App Store free of charge. You can also create documents in PDF or ePUB format on iBooks Author. The iBook format is based on the ePUB design, but distinguishes itself through differences in CSS characteristics.

Broadband eBook (BBeB)

Broadband eBook (BBeB) is a group of proprietary file formats that were developed by Sony and Canon specifically for the publication of electronic books. BBeB variants like LRF and LRX were used on early Sony devices, which were widespread across the US. But since 2009, Sony has completely revolutionized its e-books store, replacing all BBeB formats with ePUB instead. As a result, BBeB has no real use among today’s modern e-book formats.

FictionBook (FB2)

The e-book format FictionBook (.fb2) is particularly popular in Russia. This open standard is based on XML and is supported by free e-book reader programs like FBReader, Okular, CoolReader, and STDU Viewer. Since meta data like author details, title, and ISBN are saved directly in the e-book file, FB2 makes it easy to manage digital documents. But DRM functions are not supported by FictionBook.

eReader (PDB)

PDB is an e-book format that was originally developed for the Palm handheld organizers (Personal Digital Assistants, PDAs). They were used in e-book formatting by the US publishing company Barnes & Noble. In addition to the in-house software eReader, there are other viewer programs for a variety of platforms. But today, Barnes & Noble sells all its e-books in ePUB format; PDB is no longer used commercially.

Additional file formats

In addition to specific formats for displaying electronic books, most e-readers also support popular file formats like DOC, TXT, HTML, or RTF, which are used on PCs for word processing. These formats usually play a lesser role in the commercial preparation of e-books, however. Another option is the flexible, industry-standard Portable Document Format (PDF), which enables easy fixed sharing of documents on different devices. The non-text file format Comic Book Archive has also established itself for displaying digital picture books and comics.

  • PDF: the Portable Document Format (.pdf) developed by Adobe Systems is a cross-platform file format that enables digital documents to be shared regardless of the software or hardware originally used for reference. A PDF document can be viewed on devices exactly as it was created by the author. All that’s needed is PDF software, which is normally available on your e-book reader. But as a file format for electronic books, PDF is quite limited. Admittedly, it gives the format a great reach and supports DRM functions, but the rigid format, optimized for print versions, isn’t ideal for use on portable devices, even with the built-in zoom function.
  • Comic Book Archive: this non-text format is designed for displaying image sequences, particularly those used in comic books. Comic Book Archive files normally consist of a series of images in PNG or JPEG format that are saved in a shared ZIP file (.cbz). Archiving through RAR (.cbr), 7z (.cb7), TAR (.cbt), ACE (.cba), TrueCrypt (.cbtc), and Mac OS X Bundle (.cvbdl) is possible. If your reader doesn’t support Comic Book Archive format, you can unzip the archive files and open them with any regular image viewing software.

Which e-book format is right for you?

Despite the diverse technical options available to help you publish your digital book, the e-book market is really dominated by three formats. While Amazon is going its own way with KF8, all the other big players in the e-book industry have opted for ePUB. This creates a problem for authors and publishers: if you publish books in the Amazon format, you can only reach users of the Kindle series and the corresponding Kindle reader apps. The reach is greater for e-books published in ePUB format. But by using ePUB, you’re committing to ignore the market leader and the biggest online retailer in the US, because ePUB-formatted e-books can’t be opened on Kindle devices or apps. 

There is an alternative: PDF. The Portable Document Format is supported by all modern e-book readers and so can be viewed – in theory at least – on PCs, laptops, tablets, and smartphones. But there’s a catch to the lack of platform optimization: PDFs have a very rigid layout and don’t always immediately fit to every display screen size. This causes the most issues on mobile devices like smartphones, where there are a number of slightly differently sized small-screen displays. So if you want to focus on e-book readers specifically, it’s worth considering publishing your electronic book in one or both of the specialized formats, KF8 and ePUB. But if your content is designed to be read on a PC first and foremost, perhaps even to be printed out, then the flexible PDF format is a very good option.

The question of the distribution channel is also relevant. If you want to take advantage of the Amazon network and its huge customer base, then you’ll need to use their KF8 format. The same is true of Apple iBooks as well as other e-book shops – even ones that don’t use their own proprietary format.

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