Difference Between EPUB, MOBI, AZW, IBA, and PDF eBook Formats

In this article, we delineate the distinctions among several file formats utilized for eBooks, namely EPUB, MOBI, AZW, and PDF.


Girl reading e-book in sunny evening, selective focus.

Up until a few years ago, the majority of readers of eBooks were members of a niche audience. During this time, Project Gutenberg emerged as one of the pioneering initiatives aimed at digitizing books into electronic formats. The predominant format for electronic text at that time was PDF (Portable Document Format).

In the present day, eBook readers have become mainstream, and a multitude of eBook formats are now available. Whether you use eBook reading apps on your Android device or other platforms, authors, readers, and publishers now have an abundance of options when it comes to selecting popular eBook formats.

The plethora of available formats can be overwhelming and confusing at times. However, investing time to comprehend the distinctions between various file formats, notably EPUB, MOBI, AZW, IBA, and PDF eBook formats, can alleviate any confusion and enhance your eBook reading experience.


epub format
Image: Soda PDF.

Among all the eBook formats, EPUB stands out as the most prevalent and enjoys widespread support across various platforms. It is compatible with numerous eReaders, including Apple’s iBooks, Kobo, Adobe Digital Editions, Barnes & Noble’s Nook, and Aldiko on Android, to name just a few. Approximately 300 eReaders extend support for .epub files. Although Amazon Kindle does not currently support EPUB (except for the Kindle Fire tablet), there are indications that this may change in the near future.

Note: If you possess a book in the EPUB format that you wish to read on your Kindle device, you have the option to convert the eBook into a different format using a tool like Calibre.

Notably, the EPUB format adheres to an open standard, denoting its accessibility and availability to the public free of charge. However, there are specific regulations governing its use. This open standard is maintained by the International Digital Publishing Forum (IDPF), a global organization dedicated to trade and establishing standards within the digital publishing domain.

EPUB boasts the capacity to display reflowable content, enabling it to adjust its presentation to suit the output device. Additionally, it can also accommodate fixed-width layouts. In terms of appearance, EPUB closely resembles HTML-rendered pages, complete with images for a visually engaging reading experience.


The Mobipocket eBook format, commonly known as Mobi eBook, is yet another open standard utilized for eBook publishing. Notably, Amazon acquired this format, making it closely associated with the company. Mobi eBooks are cross-platform and can carry file extensions .prc or .mobi.

Mobi formats possess the capability to handle intricate content, incorporating advanced navigation controls and supporting indexing. Additionally, they boast a high degree of compression, contributing to efficient file sizes. Readers engaging with Mobi eBooks can undertake various interactive actions, such as adding personalized pages, freehand drawings, annotations, highlights, bookmarks, corrections, and notes, provided their devices support these features. Furthermore, Mobi eBooks can also incorporate dictionaries for enhanced reading assistance.

The Mobi eBook format is indeed widely supported by most major e-readers, making it compatible with various devices. However, there is one notable exception—the Barnes & Noble Nook does not support the Mobi format. Nook devices typically use the EPUB format as their primary eBook format.

One aspect to consider is that Mobi formats are particularly well-suited for smaller screens due to the image size limitation, which is set at 64K. Consequently, this format may not be as suitable for larger display devices like tablets, where the image size and format (GIF) might present some limitations.

Similar to the EPUB format, Mobi can also present reflowable content, dynamically adjusting its layout to accommodate different screen sizes, as well as a fixed-width layout for consistent formatting. This flexibility caters to various reading preferences and device specifications.


amazon kindle paperwhite.
Image: Digital Trends.

Amazon developed the AZW format as a proprietary eBook format specifically for use with their Kindle eBook reader. It is based on the MOBI format but incorporates several improvements, including better compression and encryption features.

AZW files are widely supported on various platforms that have Kindle reading apps, allowing users to access their Kindle books on different devices aside from Kindle eReaders. However, AZW files can only be acquired from the Amazon online bookstore.

One important aspect of the AZW format is its DRM (Digital Rights Management) protection, which restricts copying and unauthorized distribution of the eBook. When a Kindle eBook is purchased from Amazon, it is tied to the user’s account and the specific device ID, ensuring that it can only be accessed and read by the purchaser on their registered Kindle devices or Kindle reading apps. This DRM protection helps safeguard the intellectual property of authors and publishers but can also limit the flexibility of eBook usage.

It is worth noting that some AZW files are DRM-free, and they are essentially the same as MOBI files in terms of their underlying content format. DRM-free AZW files can be easily read on compatible eReaders and apps that support the MOBI format. However, it is essential to respect copyright and usage rights when dealing with eBook files, and users should only obtain and distribute eBooks from legitimate sources and in compliance with applicable copyright laws.


The Portable Document Format (PDF), developed by Adobe, stands as one of the oldest and most widely used eBook formats. It became an open standard in 2001, contributing to its widespread adoption and compatibility across various devices and platforms.

PDF supports both fixed-width layout and reflowable content, offering versatility in displaying eBooks and other types of documents. Due to its prevalence, numerous tools exist to create, edit, and secure PDF documents, enhancing its popularity as a reliable format for archiving and sharing information. For instance, webpages can be easily converted to PDF, allowing users to maintain an archive of online content.

PDF files offer robust security features, enabling digital signatures and protection against unauthorized editing. These security capabilities have further contributed to the widespread use of PDF files, making them suitable for various professional and legal purposes. Additionally, PDF files can be viewed and printed on virtually any platform, ensuring accessibility across different devices and operating systems.

One key advantage of the PDF format is its ability to preserve the original layout of any document, regardless of its content type. Whether the document contains text, drawings, multimedia elements, videos, 3D models, maps, full-color graphics, photos, or even complex business logic, PDF files maintain the integrity of the document’s layout and presentation. This aspect makes PDF a preferred choice for sharing documents that require accurate and consistent formatting.


Apple iBooks.
Apple iBooks.

The IBA (iBooks Author) format is another proprietary eBook format, specifically designed for books created using Apple’s iBooks Author app.

Technically, the IBA format shares similarities with EPUB. However, it incorporates custom widget code that relies on the Apple Books app’s functionality for proper functioning. As a result, IBA files are not universally compatible with all e-readers, limiting their accessibility compared to more widely supported formats like EPUB.

It is important to note that the IBA format is exclusive to books created using Apple’s iBooks Author app. If you purchase regular best-selling eBooks from the iTunes store, they will be delivered in EPUB format (though they may be DRM-restricted).

The iBooks Author format offers support for various multimedia elements, including video, sound, images, and interactive elements, making it an ideal choice for creating engaging and interactive eBooks within the Apple Books ecosystem. However, users should be aware that IBA files may have limited compatibility outside of Apple’s ecosystem and may not be readable on all e-reader devices or applications.

Other Notable E-Book Formats

Let’s take a look at some less common eBook formats:


These are file extensions for the Broad Band eBook format created by Sony for its own range of eBook readers. LRS is now an open standard, but LRF and LRX remain closed. Sony has abandoned all three formats in favor of the more widely adopted EPUB format.


The FB2 format, an XML-based format originating in Russia, is popular among eBook collectors due to its ability to store metadata within the eBook file itself. It is also commonly used as a storage format because of its ease of conversion into other formats.


DJVU is popular in the scientific community because it offers approximately 10 times better compression than PDF. It can store more than 100 black-and-white scans in less than a megabyte, making it ideal for storing large volumes of scanned documents efficiently.


LIT was Microsoft’s proprietary eBook format, but it has been discontinued since 2011. When DRM-enabled, LIT books were only readable on the Microsoft Reader app, which has also vanished in recent years.


The Rich Text Format (RTF) is compatible with virtually every e-reader on the market. It has an advantage over plain TXT files because it can retain special characters and supports reflowing and text formatting, making it a versatile choice for eBooks.

Each of these formats has its own unique characteristics and use cases, and understanding them can be beneficial when dealing with eBooks from different sources and for various purposes.