EPUB vs PDF vs MOBI: Best E-book Format

The Big Three E-book Formats

E-books come in three main formats—EPUB, PDF, and AZW3 (this is the proprietary Amazon format that has replaced MOBI). Each one serves a slightly different purpose, and they aren’t interchangeable in every situation. EPUB is the flexible, modern choice that works on most devices. PDFs lock down layouts for exact formatting, making them great for things like study guides or design-heavy materials. Then there’s MOBI, which was traditionally tied to Kindle devices but has been replaced by Amazon’s newer formats: AZW3 and KFX.

What Is EPUB?

EPUB, short for "Electronic Publication," is an open-source e-book format designed to work almost everywhere. It’s like the universal translator of e-books—it adapts easily to different devices, which is why it’s so popular.

An awesome feature of EPUB is reflowable text. That means the words on the page rearrange themselves to fit any screen size, whether you’re reading on a smartphone, tablet, or e-reader. You won’t have to squint or scroll awkwardly to read a sentence.

EPUB also supports extras like interactive content, hyperlinks, bookmarks, and embedded audio or video. It’s also supported by major platforms like Apple Books, Google Play Books, Kobo, and even Kindle (when sent via email). It doesn’t tie you to a specific platform or device, so it’s versatile and widely available.

Kindle’s E-Book Journey

MOBI started as an e-book format for early e-readers, and Amazon adopted it for Kindle. It was pretty advanced at the time, but over the years, it became outdated.

Amazon has moved on from MOBI to more advanced formats like AZW3, AZW4, and KFX. These formats are exclusive to Kindle devices and bring improvements like faster loading, better graphics, and enhanced DRM (digital rights management) to protect content. MOBI files still work on Kindle, but they’ve been phased out in favor of these newer options.

PDFs for E-Books

PDFs preserve the exact layout, fonts, and graphics of the original document. This makes them ideal for e-books with a lot of visuals, like manuals, textbooks, or anything that relies on detailed formatting. The downside is that PDFs aren’t reflowable. On smaller screens like a Kindle or smartphone, you’ll find yourself zooming in and out to read the text, which can get annoying very quickly. For simple reading, they’re just not as user-friendly as EPUB or MOBI.

Despite these drawbacks, PDFs are perfect for situations where maintaining the original layout is crucial. If you’re studying something with charts or diagrams, or you need to print out pages, PDFs are a great choice.

Choosing the Best Format for Kindle

Kindle devices have traditionally favored their proprietary formats like MOBI, AZW3, and KFX, but the addition of EPUB support has made things much easier. Now you can transfer EPUB files directly to Kindle without needing to convert them first. PDFs also work, but they’re harder to read unless specifically formatted for e-readers.

If you’re stuck with a PDF, don’t worry. Smallpdf’s Edit PDF tool can help you resize and align text and even delete unnecessary images for better readability on Kindle. It’s a quick fix that can save you from endless zooming and scrolling, but only if the file isn’t protected.

Answering Common Questions About E-book Formats

Is a Kindle book the same as an e-book?

Not exactly. All Kindle books are e-books, but not all e-books are Kindle-compatible. Kindle books are designed to work on Kindle devices or apps and often come in Amazon’s proprietary formats. If you try to open a Kindle book on another e-reader, it likely won’t work unless you convert it.

What e-book format does Kindle use?

Kindle primarily uses formats like AZW3, KFX, and now supports EPUB as well. MOBI files still work, but they’re considered outdated. While PDFs can also be opened on Kindle, they don’t always offer the smoothest reading experience unless optimized.

Which is better on Kindle, EPUB or PDF?

EPUB is generally better because it adjusts to the screen size and feels like a natural fit for e-readers. PDFs can work, but they’re fixed in their layout, making them tricky to read on smaller screens. That said, if your content is more visual-heavy—like a study guide or manual—a well-optimized PDF might still be the better option.

What is the difference between Kindle edition and PDF?

A Kindle edition is specifically designed for Amazon’s e-readers, with features like bookmarks, adjustable text sizes, and syncing across devices. PDFs, on the other hand, are static files meant to preserve the exact layout. While both can be read on Kindle, the experience will be quite different.

Which is better, an e-book or a PDF?

For reading, e-books like EPUB or Kindle editions are miles ahead because they adapt to your device. PDFs, however, are unbeatable for maintaining formatting, especially if you need to print or share the document. If you’re just curling up with a good book, stick with an e-book format.

Can I read any PDF book on Kindle?

Yes, but it’s not always a smooth ride. Some PDFs work fine, while others might require constant zooming to make the text readable. The trick is to optimize the PDF before transferring it to Kindle—resize it or crop the margins so it fits better on the screen.