A small guide to eBook file formats: which one is right for you?

These days, you can find pretty much every book in digital format, from school textbooks to children’s picture books, novels, and self-help books. And that, of course, is a good thing. E-books make knowledge more accessible, and they’re great for when you’re on-the-go. You can read at home, in school, or on your daily commute.

However, when you first go from reading only in print to reading in digital format, you might be confused by the wide variety of formats available. Apart from the formats that sound familiar, such as .txt and .pdf, you’ll see new ones, such as .mobi, .epub, and .azw. What do all these mean? Is one format superior to another? Should you save a digital eBook copy into multiple formats just to be safe? Read on to find out.

Types of e-Book formats:

Depending on the device where you open the file, you may need to choose one e-Book format over another. Besides those, there are also formats that are accepted across all devices. Here are the most popular ones:


ePUB is the most used format when it comes to publishing digital books. If you look for eBooks, you’ll find that ePUB is the default version. This format is so popular because it supports HTML5, CSS, and even JavaScript, which means that it allows for lots of flexibility in terms of styling in formatting. The best thing about the ePUB format is that the text adjusts dynamically to the size of the screen, so you’ll have the same pleasant reading experience no matter if you open the book on a tablet or smartphone.

ePUB even supports multimedia elements such as images and videos, making it perfect for interactive books too. If you plan to download some children’s books, this is the format to go with. However, one downside of ePub files is that they’re not compatible with Amazon eBook readers. Yes, that includes Kindle, which happens to be the world’s best-selling eBook reader, so if you have a Kindle or plan on buying one, you’ll have to look for other formats. Don’t worry; there are other options too.

Amazon Kindle formats: MOBI, AZW, KF8:

If you have a Kindle eBook reader, you won’t be able to open ePUB files. Instead, you’ll have to download eBooks in one of Amazon’s formats: MOBI, AZW, or KF8. Out of these three, KF8 is the best one in terms of features and layouts, and it was released along with Kindle Fire. The other two, MOBI and AZW, are good too, but they have fewer layout options, and they’re not compatible with complex visual and interactive elements. On the other hand, KF8 supports HTML5 and CSS3, which makes it perfect for children’s books and graphic novels. In the future, it is estimated that KF8 will replace MOBI and AZW.


Here’s a format that isn’t specifically associated with eBooks. PDF has been around for a while now and, if you receive things such as employee handbooks, guides, and schoolbooks, they probably come as PDF files. The good news is that you can import these files to your eBook reader can they’ll work right away. You’ll be able to view the document exactly as it was created by the author.

However, PDF on eBook readers does have its downsides. If you open an ePUB and PDF file on an eBook reader side by side, you’ll see that the PDF file looks a bit off and doesn’t feel “native.” That’s because the file doesn’t adjust to the size of the screen. And yet, many people want to use PDF for simple documents because the format is compatible with any device. Also, if you want to share a digital book with someone else but you don’t know what device they are using, the safest thing to do is convert it to PDF. Fortunately, that’s simple to do and doesn’t require advanced skills. eBook readers don’t have built-in converters, but you can find an ePUB to PDF converter online and convert the file straight from your browser.


Although Apple was late to join the eBook club, they eventually came with their own format: iBooks. This format is based on the ePUB design, but it has a few CSS characteristics. If you download eBooks from Apple’s store, they’ll come in this format. Overall, it has some excellent layout options, and, as Apple has used us by now, the reading experience is smooth on the iPad. If you’re deep into the Apple ecosystem, this is probably the format to go with. However, like pretty much everything else does, iBooks is an exclusive format, and if you want to open the same book on a non-Apple device, such as a Kindle or a Windows laptop, you won’t be able to do that. When in doubt, download the books in ePUB format because Apple devices support that too.

Apart from these popular eBook formats, you also have some “underdogs,” such as:

  • Comic Book Archive – created specifically for comic books
  • PDB – this is an old format used by Barnes & Noble, which is no longer in use and was replaced by ePUB
  • FictionBook – this is a popular format in Russia, supported by free e-book reader software such as Okular and CoolReader.
  • Broadband eBook – initially used by Sony, this is another old format that got replaced by ePUB.
  • Text files – the plain old .txt file also lends itself to e-reader use, and it’s not the worst option you can use if you have text-heavy files. However, keep in mind that it has basically zero formatting options, and .txt books are painstakingly boring to read.

These last file formats are quite rare these days, but you never know when you might come across them. For example, if you’re looking for an old textbook or you’re cleaning up your digital library from a few years ago, you might find some formats that aren’t in use anymore. In these cases, it’s good to have an online converter in your bookmark toolbar. Plus, if you download an eBook into one format but don’t like it, you can always convert it to something else.

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