Various Document File Formats for Ebook Readers

Below is a summary of the major differences of formats used to create and publish e-Books


In the eBooks world, the EPUB format is perhaps the most adopted of all formats.

EPUB is an open standard format for eBook publishing designed by the International Digital Publishing Forum (design by committee).

  • Device – iOS, Blackberry devices, Kobo eReader, Android and almost all other notable eBook readers. However, not supported by Amazon kindle.
  • Functionality - can display reflowable content i.e can adjust its presentation to the output device


However, EPUB has two major shortcomings. First, files are based on XHTML and CSS cascading style sheets and can look different on different machines. Secondly, EPUB doesn’t require DRM (Digital Rights Management) but allows it, so protected books may be read on the otherwise perceived “wrong” system.


Mobi-pocket was purchased by Amazon in 2005 from a French company which first developed this reading software at a time when eBooks where still in their infancy.

  • Devices – You can use on any of the kindle devices or any kindle app.
  • Extensions - .mobi, .prc, and .azw [There’s no functional difference between these formats]
  • Add-on - Dictionary


This format can take complex content, include advanced navigation control, allows for indexing and offers a high degree of compression.

MOBI is suited for smaller screens but image size is limited to 64K.


AZW is a proprietary format developed by Amazon specifically for the Kindle eBook reader, its popular device.

It is a modification of MOBI but with better compression and encryption. This has made it simple to convert a MOBI file into AZW format and DRM-Protected books can be downloaded in kindle format. However, AZW is locked to the device ID which is registered automatically with the user account of the Kindle purchaser.


Invented by Adobe systems, PDF (Portable Document Format) was developed to provide a platform-independent means of exchanging fixed-layout documents.

Widely preferred because of this ability to preserve the original layout of document e.g. texts, drawings and maps, multimedia, full-color graphics, photos or even business logic.

It was made an open source from 2001.

  • Devices – Can be read on most eBook devices but none of the retailers will sell a PDF to consumers.
  • Code – PDFs are created with proprietary codes. Additionally, they are not built on HTML therefore original source files must be edited.


The main problem PDF files have in the modern eBook world is that the text in this format cannot reflow to fit small screens. As a result, when a file is loaded on a device it needs to be zoomed in to be readable, forcing the user to scroll left and right from time to time.

However, an updated format called PDF/UA released in 2012 has reflow features but has only got moderate support from third party hardware and software manufacturers.


The practical upshot of these file format confusion entails that you need to choose which retailer you prefer to buy from upfront and then stick with it.

Fortunately, both Amazon and Barnes& Noble offer similar selection of eBooks from the major publishers and the best news is that there exist tools that can help convert PDF to EPUB, MOBI or HTML or convert PDF for kindle readers.