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What is the Best Ebook Format?

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Table of Contents

Introduction

Ebooks are now a staple of modern reading habits, reshaping how books are published, distributed, and consumed. With the surge in digital publishing, choosing the best ebook format has become a pressing concern for publishers, authors, developers, and even readers. Each format comes with its own advantages, limitations, and use cases. EPUB, PDF, AZW3, and even newer formats like Apple’s proprietary IBA have carved out their niches in this diverse ecosystem. But amid all the options, here’s a perennial question: What is the best ebook format?

The answer depends on your perspective—what works for a publisher may not work for a developer or a reader. That’s why this article takes a deep dive into the core formats dominating the ebook world, explaining their strengths, weaknesses, and ideal scenarios. We’ll also explore the underlying technologies, platform compatibility, formatting capabilities, and file management considerations influencing which format rises to the top in specific contexts. By the end, you’ll understand what “best” means in the ever-evolving landscape of ebooks.

A Brief History of Ebook Formats

The evolution of ebook formats parallels the rise of digital media. In the early days, ebooks were often plain text (.txt) files—barebones, unstructured, and unfriendly for any kind of rich reading experience. As demands grew for better formatting and multimedia support, more sophisticated formats emerged.

PDF (Portable Document Format), introduced by Adobe in the 1990s, became a foundational digital document format. It wasn’t created specifically for ebooks, but it allowed precise layout control and became a go-to option for sharing books in a digital format. Then came formats specifically engineered for ebooks—like MOBI (phased out in 2022), originally developed by Mobipocket, and EPUB, backed by the International Digital Publishing Forum (IDPF).

Kindle’s rise in the late 2000s added new dynamics. Amazon adopted MOBI and later introduced its own formats, including AZW and AZW3, which were based on MOBI but included DRM and other proprietary features. Meanwhile, EPUB emerged as the open-standard alternative, widely supported outside Amazon’s walled garden.

This fragmented history helps explain why the ebook world today still juggles multiple formats, each shaped by its origin and purpose.

EPUB: The Open-Standard Workhorse

EPUB (Electronic Publication) is arguably the most versatile and widely adopted ebook format today. As an open standard maintained by the W3C (after absorbing the IDPF), it offers flexibility, compatibility, and freedom from vendor lock-in.

One of EPUB’s standout features is its reflowable text. This means the content adjusts to fit the screen size, font settings, and orientation of the reader’s device. EPUB works beautifully on smartphones, tablets, and e-readers, ensuring a seamless experience regardless of where they read. EPUB supports rich formatting, embedded images, multimedia, and even interactive content through HTML5 and CSS3.

Another advantage of EPUB is its broad compatibility. It is supported by Apple Books, Google Play Books, Kobo, and most non-Kindle e-readers. Tools like Calibre and Sigil make it easy for authors and publishers to create, edit, and convert EPUB files. With EPUB 3, there’s even support for vertical writing, MathML, and accessibility features, making it inclusive for a global audience.

However, EPUB’s Achilles’ heel is its incompatibility with Amazon Kindle devices. Kindle does not natively support EPUB, which forces publishers and readers to convert it to another format if they want to reach Amazon’s vast user base. That said, Amazon recently announced support for EPUB through its Kindle Previewer tool, indicating a slow but steady shift in the tide.

MOBI and AZW: Kindle’s Proprietary Legacy

When it comes to Kindle devices, MOBI and AZW (and its successors AZW3 and KFX) are the primary ebook formats. MOBI, the original format acquired from Mobipocket, was streamlined and customized for Amazon’s purposes. AZW added DRM and tighter integration with Kindle services.

These formats were designed with simplicity and performance in mind. While they support basic styling, their capabilities lag behind EPUB in terms of layout control and advanced formatting. AZW3 and KFX attempted to bridge this gap by supporting richer typesetting and features like hyphenation, kerning, and enhanced font rendering.

The main advantage of these formats is their seamless integration with the Kindle ecosystem. If your goal is to publish and distribute ebooks on Amazon, using Kindle-specific formats—or uploading EPUBs that Amazon converts to its internal format—is nearly unavoidable. Kindle Direct Publishing (KDP) optimizes ebooks for its platform and often wraps content into the KFX format on the backend.

However, these proprietary formats come with trade-offs. They limit your ability to distribute content outside Amazon’s system. There’s also less control over how the final file appears, since Amazon’s conversion process may alter aspects of formatting and layout. Furthermore, editing or reverse-engineering Kindle formats is tricky due to DRM and a lack of transparent documentation. MOBI eventually ended up in the trench after Amazon made it obsolete. 

PDF: Precision at a Cost

PDF stands apart from EPUB and Kindle formats because it’s not reflowable. It maintains a fixed layout that appears precisely the same on all devices, preserving fonts, images, and formatting with pixel-perfect accuracy. This makes it ideal for print-ready files, textbooks, reference materials, and academic content that relies on strict formatting.

PDF’s strength lies in its fidelity. If you’re publishing a heavily designed document—say, a scientific paper with complex tables or a coffee-table book—PDF ensures the content will look exactly as intended. It’s also universally supported, readable on virtually any device using built-in or free software like Adobe Acrobat Reader.

However, this precision comes with serious limitations in an ebook context. PDFs don’t adapt well to small screens. Reading a fixed-layout document on a smartphone or e-reader can be a frustrating experience, involving constant zooming and panning. Searchability and accessibility can also suffer if the file is not properly tagged.

From a publisher’s standpoint, PDFs are often used for proofs, submissions, and downloadable content, but not for mainstream ebook distribution. For reading convenience and modern accessibility standards, PDFs generally fall short when compared to EPUB.

Recently, Adobe introduced the liquid mode, allowing PDF content to be read in a reflowable format, similar to EPUB. With tight DRM, this can be the future. 

HTML5 and Web-Based Formats

With the rise of browser-based reading experiences, HTML5 has emerged as a compelling option, especially for interactive or educational ebooks. Instead of distributing a single file like EPUB or PDF, HTML5 ebooks are hosted on the web, allowing real-time updates, interactivity, and integration with analytics tools.

HTML5 formats support multimedia, animations, quizzes, and dynamic layouts. They’re commonly used in e-learning, digital magazines, and corporate training materials. Some platforms even offer EPUB-to-web conversion, making it easier to convert static books into dynamic environments.

The main drawback is that these ebooks require a stable internet connection unless saved for offline access using progressive web app (PWA) technologies. Also, distribution is trickier—you can’t simply upload an HTML5 ebook to a marketplace like Amazon or Google Play Books.

That said, HTML5 ebooks are highly flexible and forward-looking. For publishers exploring immersive storytelling or interactive educational content, the web is an increasingly attractive platform.

Apple’s IBA and Proprietary Formats

Apple’s iBooks Author (IBA) was once a bold move to define the future of ebooks—interactive, media-rich, and beautiful. Unfortunately, it came with a catch: books made in IBA could only be sold through Apple Books. Despite its intuitive drag-and-drop interface and robust feature set, this walled-garden approach severely limited its adoption.

Although Apple has since retired iBooks Author in favor of Pages (which exports to EPUB), its legacy highlights a tension in ebook publishing between innovation and openness. Proprietary formats may offer impressive capabilities, but they often come with limitations in distribution and compatibility.

This is a recurring theme in ebook technology: formats that try to do too much or lock users into a single ecosystem rarely endure. EPUB’s resilience, by contrast, comes from its openness and adaptability.

DRM: The Invisible Force Behind Ebook Formats

Digital Rights Management (DRM) plays a huge, often invisible role in shaping how ebook formats function. DRM restricts copying, printing, and sharing of ebooks. Most proprietary formats, such as AZW or Apple Books’ EPUB variants, have built-in DRM mechanisms to enforce licensing terms.

While DRM protects publishers and authors from piracy, it also hampers the reader experience and limits device compatibility. A reader who buys an ebook on Amazon can’t read it on a Kobo e-reader unless the DRM is stripped—a process that’s technically complex and legally grey.

Therefore, the best ebook format is not just about layout and features but also about user freedom. Open EPUB files without DRM can be backed up, converted, and read on any device. DRM-locked files, regardless of format, reduce ownership to a license agreement.

Accessibility and Inclusivity

The question of the best ebook format isn’t complete without considering accessibility. Features like text-to-speech, screen reader compatibility, and adjustable fonts are crucial for visually impaired or neurodiverse readers.

EPUB 3 is currently the most accessible ebook format. It supports semantic markup, ARIA roles, MathML for equations, and navigation landmarks—all essential for screen readers and adaptive devices. EPUB also aligns with global accessibility standards like WCAG and the Marrakesh Treaty.

PDFs can be accessible, but only if meticulously tagged and structured. Many aren’t. Kindle formats lag in this area, partly because of their proprietary nature and limited support for accessibility metadata.

If accessibility is a core concern, EPUB is the clear leader in the field, provided it’s correctly authored and validated.

The Publisher’s Perspective

From a publishing standpoint, choosing the best ebook format often involves balancing reach, production costs, and user experience. EPUB is typically the most efficient and scalable option. It’s supported by most major platforms (except Kindle, which can still convert it) and enables a rich reading experience without heavy development work.

What is the best ebook format - Kindle

For academic publishers, EPUB also allows embedding citations, linking to references, and providing accessibility—all critical in scholarly contexts. For trade publishers, EPUB files can be sold through multiple online stores without worrying about vendor lock-in.

That said, publishers targeting Kindle readers cannot ignore AZW. While Amazon now accepts EPUB uploads, it converts them into Kindle formats behind the scenes. Understanding how that conversion affects formatting, layout, and media is still necessary for quality control.

PDFs remain essential for print production and institutional use, especially when document fidelity is non-negotiable. However, as a general-purpose ebook format, they are increasingly outdated.

So, What Is the Best Ebook Format?

Let’s not beat around the bush. If we define “best” as the most versatile, open, accessible, and forward-compatible format, then EPUB takes the crown. It adapts to different screen sizes, plays nicely with multiple platforms, supports multimedia and accessibility, and doesn’t tie you to a single vendor.

That said, context matters. If you’re publishing for Kindle only, you’ll have to work within Amazon’s format ecosystem. If you’re producing a richly designed coffee-table book, PDF might be the only format that delivers your vision without compromise. If you’re pushing boundaries with interactive educational material, HTML5 may be the most innovative route.

In short, the best ebook format is the one that fits your goals, your audience, and your platform strategy.

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