A Guide to Formats

Electronic book file formats have come a long way since their inception. From simple text files, they have evolved into complex multimedia formats. Today, there are a variety of e-book file formats available for different purposes. While some formats, like TXT and HTML, may be more suitable for simple text documents, others, like PDF and EPUB, offer more advanced features for complex documents. MOBI and AZW3 are optimized for Amazon Kindle devices, while Word document formats are commonly used in publishing. Since each format has its own unique features and advantages, it is important to know and consider its strengths and weaknesses. This article provides readers with an overview of popular e-book formats, including their features and compatibility with electronic devices.


Historically, the TXT format was the first file format used for electronic documents. It remains a popular format for e-books due to its simplicity and ease of use. One of its advantages is that it can be read on any device, making it a universal format. However, there are some limitations to using the TXT format for e-books. For instance, it lacks formatting, images, and other multimedia elements, making it unsuitable for complex documents or books with illustrations.

When working with TXT files, it is important to consider the encoding of the text. The encoding determines how characters are represented in the file and can impact how the text is displayed on different devices. Different languages may use different encodings, and failing to account for this can result in garbled text.


HTML is a widely used format for electronic books due to its flexibility and ease of use. One of its strongest features is that it allows for multimedia content, such as images, audio, and video, to be embedded directly into the e-book. This makes it an ideal choice for books that require a lot of visual content or for educational materials that need to include interactive elements. Additionally, because HTML is a web-based format, it can be viewed on any device that has a web browser, making it accessible to a wide audience.

However, HTML does have some drawbacks when compared to specialized eBook formats like EPUB and MOBI. One of the main issues is that it can be difficult to control the layout and formatting of the content. This can make it challenging to ensure that the book looks the same across all devices and platforms. Additionally, HTML lacks some of the advanced features found in eBook formats, such as support for reflowable text and the ability to add annotations and bookmarks.


PDF (Portable Document Format) is a popular file format for presenting electronic documents and publications, including e-books. It was developed by Adobe Systems in the 1990s and has since become a widely used standard for distributing documents that can be viewed and printed on different devices and platforms. One of the main benefits of using PDF for e-books is that it preserves the layout and formatting of the original document, ensuring that the text, images, and other elements appear exactly as intended by the author.

PDF was one of the first formats to implement DRM technology, which allowed publishers to control access to their content and prevent unauthorized copying and sharing. The DRM technology for PDF files is called Adobe Content Server and is widely used by publishers of e-books, magazines, and other digital content.

PDF has both strong and weak points compared to specialized e-book formats such as EPUB and MOBI. On the one hand, PDF is a universal format that can be opened and viewed on almost any device without the need for specialized software. It also allows for easy printing and sharing of e-books. However, PDF does not support reflowable text, which means that the content is fixed in size and may not adjust well to different screen sizes. This can make reading on small screens difficult and uncomfortable. Additionally, PDF files can be relatively large, which may result in slower download times and take up more storage space on devices. Finally, PDF does not support many of the interactive features that are available in specialized e-book formats, such as audio and video.


EPUB (Electronic Publication) is an open standard format for digital books, which was first introduced by the International Digital Publishing Forum (IDPF) in 2007. The format was designed to be flexible and support reflowable content, which means that the text can automatically adjust to fit the size of the screen, whether it's a small smartphone or a large tablet. This makes it much easier to read an e-book on different devices, without having to zoom in or scroll horizontally. EPUB is based on XML, XHTML, and CSS, and it can include both text and images, as well as multimedia elements like audio and video. EPUB also supports features like bookmarks, annotations, and a table of contents, making it easy for readers to navigate through the content.

However, despite its great popularity, there are certain limitations to EPUB format that make it less suitable for certain types of content. For example, EPUB does not support complex layouts, such as those found in technical manuals, and it can also struggle with handling large amounts of multimedia content. DRM implemented in EPUB format can be considered sufficient for most common needs, but it may not be enough for some more advanced use cases. Some publishers and authors may require more advanced DRM solutions to protect their content.


The MOBI format was first introduced in 2000 by the French company Mobipocket. The format was developed for use on mobile devices, specifically for their Mobipocket Reader software. The idea behind the format was to create a file format that could support rich text and images, while still being lightweight and easy to load on mobile devices with limited storage capacity. In 2005, Amazon acquired Mobipocket and began using the MOBI format as the standard file format for their Kindle e-reader devices, which helped to increase the format's popularity. The MOBI format is still supported by the Kindle platform, and is widely used for e-books as it supports a variety of features such as bookmarks, annotations, and syncing across devices.

One of the advantages of MOBI format over EPUB is its ability to display graphics and tables more effectively. MOBI also has a simpler and more limited formatting system, which can be an advantage for some publishers who want more control over how their books appear on different devices. However, MOBI does not support some of the more advanced features of EPUB, such as video or audio embedding, and its text formatting options are limited compared to EPUB. While MOBI has some advantages over EPUB, it is not as versatile and widely supported as the EPUB format.


AZW and AZW3 are two proprietary eBook formats developed by Amazon. AZW was introduced in 2007, while AZW3 (also known as KF8) was launched in 2011. These formats were created as an improvement over the MOBI format to address some of its limitations, such as lack of support for advanced formatting options and limited capabilities for formatting images and other media.

One of the strengths of the AZW and AZW3 formats is their tight integration with Amazon's Kindle platform, which provides seamless synchronization of user data across multiple devices. Additionally, these formats offer support for advanced typography and layout features, making them ideal for complex books with intricate formatting, such as textbooks and technical manuals.


CBR and CBZ are digital comic book formats that have become increasingly popular in recent years. CBR stands for 'Comic Book Reader', while CBZ stands for 'Comic Book ZIP'. These formats were specifically designed for comic books and other graphic novels. CBR and CBZ files are essentially collections of high-resolution images that are compressed into a single file. CBR files are typically compressed using RAR compression, while CBZ files are compressed using ZIP compression.

CBR and CBZ files can be read on a variety of devices, including smartphones, tablets, and computers. There are a number of dedicated comic reader apps available for iOS and Android devices. In addition, many e-book reader apps, such as Calibre and Amazon Kindle, also support these formats.

CBR and CBZ files are easy to create and share, making them a popular choice for independent comic book creators and publishers. However, CBR and CBZ files do not support the same level of interactivity and customization as some other e-book formats, such as EPUB and MOBI.

Word document formats

Microsoft Word formats, such as DOC, DOCX, and RTF, can also be used for e-books. These formats allow for complex formatting, including images and multimedia elements, and are widely used in publishing. However, they are not optimized for e-book reading and may have formatting issues on different devices. In addition, they are not as portable as other e-book formats and require special software to read. Thus, for e-book publishing, specialized e-book formats such as EPUB and MOBI are generally the best choice as they offer more advanced e-reading features and optimizations.