Book Formatting File Types Explained

Over the years, there have been many file types used to create books, from eBooks to Print Books.

Those file types evolve, some are discontinued, but one in particular currently reigns supreme. (Hint: it rhymes with MEHUB).

In this article, you will learn:
  1. The most common file types for eBooks and print
  2. Other file types common for ebooks
  3. Which file types you should use

There are three primary book file types that you should be familiar with, though one of them is already on its way out.

EPUB (.epub)

epub file formatting type

An EPUB file is the most widely used, and best supported format for an eBook. It plays on virtually all devices, including:

  • Kindle
  • Nook
  • Computers
  • Tablets
  • Smartphones
  • Most ebook readers

Most EPUB files are reflowable, which means that the text and images will shift to fit the screen size of the device.

However, this doesn’t have to be the case. EPUBs are versatile enough that they can be programmed to have fixed layouts if needed.

A fixed layout usually has designs that are dependent on the layout of the text and images. These layouts are common in children’s books, image/infographic-heavy non-fiction books, and comic books.

Thankfully, you can have both reflowable and fixed layout books with EPUB.

EPUB book files are based on coding standards such as XHTML, XML, CSS, and compatible with HTML5, MathML, JavaScript, and vector graphics like the popular SVG file type.

In other words, it’s a powerful file.

Formerly, EPUBs were not published on Amazon, requiring the MOBI instead. But that has since changed. EPUBs can now be used on Amazon, and are now the recommended ebook type there.

When Should You Use an EPUB file?

Since almost all ebook vendors use EPUB files these days, you should default to the EPUB in almost every instance where you would need an eBook.

Print, however, is another matter…

PDF (.pdf)

PDF book formatting file type

PDFs are another common type of book file. However, they are better served in constructing your print books, and not as eBooks.

The PDF was a file type created by Adobe, and has gained widespread use ever since. They are useful for any book that requires a fixed layout, especially in print.

When Should You Use a PDF?

You should use a PDF when uploading a print book to Amazon, IngramSpark, or another print service. They should never be used as eBooks. If you need the fixed layout that a PDF can provide, use the fixed EPUB format.

MOBI (.mobi)

Mobi book formatting file type

Previously, the MOBI file was another important file type to be aware of, as it was the primary file used for uploading a book to Amazon’s KDP Marketplace.

However, all that has changed.

Amazon now accepts, and even recommends, that you upload your book as an EPUB.

We still include MOBI files here, though, because they are still accepted by Amazon for fixed-layout books, which you might want. Since the conversion process of one eBook format to another can cause problems in the layout, this could be a great way of ensuring that everything looks right before submitting to Amazon.

That said, the MOBI is all but dead.

Amazon now has two other eBook formats, AZW3 and KPF, which are the primary book file formats that Amazon uses on the user end.

When you submit a MOBI, EPUB, DOCX, or any other accepted file type to Amazon, it will usually convert to AZW3 or KPF.

AZW3 (.azw3) and KPF (.kpf)

AZW3 and KPF are worth knowing because they are the primary file types used by Amazon today, using their own digital rights management (DRM) system..

  • AZW3, also known as KF8 is the eBook file that Amazon uses on its devices. It can only be viewed on Amazon devices.
  • KPF, a variant of the older KFX file, is a file type generated using Amazon’s own book formatting software, Kindle Create.

In addition to the EPUB, KDP also recommends using a KPF file type because it will integrate seamlessly with their devices. That said, doing so is not required, and Amazon will automatically convert your EPUB to the correct format upon upload.

If you want to go the extra mile, you can convert your ebook to a KPF format ahead of time and confirm that everything works the way it should, then submit to Amazon.

However, you don’t need to worry much about AZW3 and KPF, since these are just file types that are used on their end, and the EPUB is more than sufficient for submitting to Amazon.

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Other Formats

In addition to the five formats mentioned above, here are a handful of other book file types you might encounter, though none of them are particularly significant for most authors.

  • Mobipocket: An older e-book format used by Amazon that was officially discontinued in 2016.
  • AZW: An older version of AZW3.
  • DOC/DOCX: These will work as ebooks when uploaded to KDP, but if you have even a modest amount of formatting, it very often doesn’t translate well.
  • RTF/TXT: These file types will also (technically) work with KDP, but have no advanced formatting features.
  • IBOOKS: This file type is used by Apple, but you can still use an EPUB when submitting to Apple Books.
  • FB2: This is a popular ebook file type in Russia.
  • Comic Book Archive: There are a number of file extensions that you’ll find for comic books, such as .cbz, .cbr, .cb7, and more. These are essentially ZIP files that can be unzipped to see a series of images.

For a comprehensive list of book file types, visit this page.

Which eBook Format is Best?

We have a comprehensive comparison of the main file types that you can read, but the bottom line is this:

For Ebooks

Ever since KDP allowed the use of the EPUB, it has become virtually the only ebook file type that is most compatible with all the major ebook retailers, as you can see below.

Not only that, it is also open source, extremely versatile, and widely accepted as the best version. We highly recommend that you use the EPUB as your first choice.


(no embedded formatting)

(only on the Kindle app, not the Fire tablet)

Apple Books

Barnes & Noble Press
Google Play Books

The one possible exception we would make might be a KPF file, created using Kindle Create. Using this file is one of the best ways to ensure that your book integrates seamlessly with Amazon.

That said, the EPUB works perfectly fine for most people, and it’s easy to catch any issues by using the kindle previewer when uploading to KDP.

For Print

If you are uploading to KDP Print or IngramSpark, the best option is using a PDF file. This helps you keep the fixed layout that you need for a seamless digital print experience.

A formatting software is a great way to create these print PDFs. See our recommendations for best formatting software here.

Which File Format Will You Use?

Now that you know the ins and outs of the main book file types, which one will you use? Let us know below what your experience is with these file types.

Additionally, if you want to know more about formatting or converting between files, check out these resources:

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