EPUB vs MOBI vs PDF: Which Format for Your Book?

EPUB is the right format for nearly every ebook published today. MOBI is dead, Amazon deprecated it in 2023 and no longer accepts MOBI uploads. PDF is reserved for heavily designed books where exact page layout matters more than readability across devices.

That is the short answer. The rest of this guide explains why, covers the edge cases, and gives you a clear decision framework for every type of book.

Format Comparison at a Glance

EPUB: The Universal Standard

EPUB is a ZIP file containing HTML, CSS, images, and metadata. Think of it as a self-contained website packaged into a single file. E-readers interpret the HTML and CSS to display your book, reflowing the text to fit whatever screen size the reader is using.

Why EPUB Wins for Most Books

Universal acceptance. Apple Books, Kobo, Barnes & Noble, Google Play Books, Smashwords, Draft2Digital, libraries (via OverDrive/Libby), and dozens of smaller retailers all accept EPUB. Even Amazon accepts EPUB uploads through KDP, they convert it to their KF8 format server-side.

Reflowable content. Readers can adjust font size, font family, line spacing, and margins. This matters more than most authors realize. A 2025 survey by the Digital Publishing Alliance found that 67% of ebook readers adjust font size from the default, and 31% change the font family. Your book needs to look good across all these combinations.

Full accessibility support. EPUB 3 supports alt text, semantic HTML, ARIA attributes, navigation documents, and accessibility metadata. This is not optional, the European Accessibility Act (effective June 2025) requires these features for ebooks sold in the EU. Amazon also factors accessibility into its ranking algorithms.

Smaller file sizes. A typical novel as an EPUB is 300KB to 2MB. The same book as a PDF can easily be 5-10MB. Smaller files download faster, take up less storage on readers' devices, and are cheaper to deliver.

EPUB 2 vs EPUB 3

If you are working with older tools, you may be producing EPUB 2 files. Here is what you are missing:

The most commercially important difference is accessibility metadata. EPUB 3 supports the full set of schema:accessibilityFeature, schema:accessibilityHazard, and schema:accessibilitySummary properties that Amazon and Apple now check for. EPUB 2 does not.

If your formatting tool outputs EPUB 2, check if a newer version supports EPUB 3 export. Tools like Vellum, Atticus, and current versions of Calibre all export EPUB 3 by default.

For a thorough look at formatting tools and their output formats, see our EPUB formatting tools comparison.

MOBI: Officially Dead

Amazon introduced the MOBI format in the early 2000s through its acquisition of Mobipocket. For years, MOBI (and its successor KF8) was the only way to get books onto Kindle devices.

That era is over. In June 2023, Amazon stopped accepting MOBI uploads to KDP. They also removed the "Send to Kindle" feature for MOBI files. KDP now accepts EPUB, DOCX, and KPF (Kindle Package Format, exported from Kindle Create).

What Happened to MOBI?

MOBI could not keep up with modern ebook requirements. It lacked proper accessibility support, its metadata capabilities were limited, and it struggled with complex layouts. Amazon's own KF8 format, which they have been using internally since 2011, is functionally an EPUB variant wrapped in an Amazon container.

By accepting EPUB directly, Amazon simplified the publishing pipeline and aligned with the accessibility standards that regulators and readers are demanding.

Do You Still Need to Think About MOBI?

No. If anyone advises you to create MOBI files in 2026, their information is outdated. Upload EPUB to KDP and let Amazon handle the conversion. If you want to preview how your book looks on Kindle devices, use Kindle Previewer 3 (free), it accepts EPUB input directly.

The one exception: if you are distributing directly to readers through your website (not through a retailer), some older Kindles may only read MOBI. But even this is increasingly rare as older devices age out of active use. A 2025 estimate from the Digital Reader puts the active pre-2012 Kindle installed base at under 3% of Kindle users.

PDF: The Layout Preservation Format

PDF (Portable Document Format) preserves exact page layouts. Every element, text, images, tables, charts, stays exactly where you put it, regardless of the viewing device.

When PDF Is the Right Choice

PDF is appropriate when your book's visual layout is integral to the reading experience:

• Cookbooks with recipe layouts, ingredient columns, and step photographs
• Art books and photography collections where image placement matters
• Children's picture books with text integrated into illustrations
• Technical manuals with complex diagrams and callouts
• Textbooks with multi-column layouts, sidebars, and margin notes
• Graphic novels and comics

When PDF Is the Wrong Choice

For text-heavy books, novels, memoirs, biographies, business books, self-help, PDF is almost always wrong. Here is why:

No reflowing. A PDF designed for an 8.5 x 11 page looks terrible on a 6-inch phone screen. Readers have to zoom and scroll horizontally, which is a miserable experience. E-readers cannot adjust font size, line spacing, or margins in a PDF.

Poor accessibility. PDFs can be made accessible, but the process is complex and most authoring tools do not produce accessible PDFs by default. Screen readers struggle with many PDF files because the underlying structure lacks semantic markup. EPUB's HTML-based format is inherently more accessible.

Larger file sizes. PDFs embed fonts and render text as positioned objects, making files 3-10x larger than the equivalent EPUB. This affects download times, storage requirements, and delivery costs.

Limited retailer acceptance. Most ebook retailers do not accept PDF uploads for reflowable ebook listings. Kobo accepts PDF for some use cases, and Google Play Books handles PDF, but Amazon KDP and Apple Books expect EPUB (or DOCX for KDP).

Fixed-Layout EPUB: The Best of Both Worlds?

EPUB 3 supports fixed-layout content, where each page has a predetermined size and elements are positioned absolutely, similar to a PDF but in an EPUB container. This gives you the layout control of PDF with the distribution advantages of EPUB.

Fixed-Layout EPUB vs PDF

Fixed-layout EPUBs work well for children's books and graphic novels. They are less ideal for text-heavy design books because the text still does not reflow, readers pinch and zoom just like a PDF.

Amazon supports fixed-layout KF8, and KDP accepts fixed-layout EPUB uploads. Apple Books also handles fixed-layout EPUB well, including support for read-aloud with media overlays.

Making the Decision: A Flowchart

Ask yourself these questions in order:

1. Is your book primarily text? (novel, memoir, non-fiction prose)

• Yes → EPUB (reflowable). Stop here.

2. Does your layout require exact positioning? (art, photography, comics)

• Yes → Continue to question 3.
• No → EPUB (reflowable). Stop here.

3. Do you need distribution across multiple retailers?

• Yes → Fixed-layout EPUB.
• No (direct sales only) → PDF is acceptable, but fixed-layout EPUB is still better for accessibility.

4. Is the content primarily images with minimal text?

• Yes → Fixed-layout EPUB or PDF, depending on your tools.
• No → Fixed-layout EPUB. The text benefits from EPUB's metadata and accessibility support.

Format Requirements by Retailer

The pattern is clear: EPUB 3 is universally accepted and universally preferred. Creating a single, well-formatted EPUB 3 file lets you distribute everywhere with one file.

Converting Between Formats

EPUB to PDF

Calibre handles this conversion well for simple books. For complex layouts, you will get better results exporting to PDF directly from your source tool (InDesign, Vellum, Atticus).

PDF to EPUB

This is almost always a bad idea. PDF-to-EPUB conversion tools try to extract text and rebuild reflowable HTML, but the results are usually poor, broken paragraphs, lost formatting, mangled tables. You are better off going back to your source document (Word, Google Docs, Scrivener) and exporting to EPUB directly.

EPUB 2 to EPUB 3

This conversion is straightforward and well-supported. Calibre can do it automatically. The main changes are: content files move from XHTML 1.1 to HTML5, a nav.xhtml file is created alongside the existing toc.ncx, and the OPF metadata namespace is updated. Rahatt's auto-fix feature also handles this conversion as part of its accessibility repair process.

Accessibility Across Formats

Accessibility is where EPUB 3 has a decisive advantage over both MOBI/KF8 and PDF.

EPUB 3's HTML-based structure supports semantic markup natively. Headings, lists, tables, and images all have proper HTML tags that screen readers understand. Adding accessibility metadata, alt text, and navigation documents is straightforward.

PDF accessibility (PDF/UA) exists but is complex to implement. Most PDF authoring tools do not produce accessible PDFs by default. You need to manually add tags, reading order, alt text, and bookmarks, a process that can take hours for a complex document.

Amazon's KF8 format supports some accessibility features, but since you upload EPUB to KDP, your accessibility work should focus on getting the EPUB right. Amazon's conversion preserves the accessibility features from a well-structured EPUB 3.

For a deeper dive into accessibility requirements and how they affect your ebook's visibility, see our EPUB accessibility 101 guide and our complete ebook formatting guide.

Frequently Asked Questions

Should I upload EPUB or DOCX to Amazon KDP?

EPUB gives you more control over formatting. When you upload DOCX, KDP applies its own conversion and styling, which can produce unexpected results. With EPUB, you control the HTML and CSS directly (or through your formatting tool), and the conversion to KF8 is more predictable. If your book is simple text with no special formatting, DOCX works fine. For anything with custom styling, images, or complex structure, use EPUB.

Can Kindle devices read EPUB files?

Not directly, but it does not matter. When you upload an EPUB to KDP, Amazon converts it to KF8 for Kindle devices. Readers using the Kindle app on iOS, Android, or desktop also receive the KF8 version. You never need to deliver an EPUB to Kindle readers, Amazon handles the format conversion.

Is EPUB 3 backward compatible with older e-readers?

Most EPUB 3 features degrade gracefully on older readers. The core content (HTML text and images) displays fine. Advanced features like media overlays, JavaScript, and some CSS3 properties may not work on older devices, but the text remains readable. Including a toc.ncx file alongside the nav.xhtml ensures navigation works on EPUB 2 readers.

What about Amazon's KPF format?

KPF (Kindle Package Format) is exported from Amazon's free Kindle Create tool. It is essentially a pre-converted KF8 package. KPF is useful if you are publishing exclusively on Amazon and want pixel-perfect control over Kindle rendering. However, it locks you into Amazon's ecosystem, you cannot use a KPF file on any other retailer. For most indie authors publishing wide, EPUB is the better choice.

My book has lots of tables and charts. Which format should I use?

Use reflowable EPUB 3 with simplified table markup. Complex tables can be challenging in reflowable formats, but simple tables (3-5 columns, basic data) work well. For very complex tables, consider converting them to images with proper alt text describing the data. If your entire book revolves around complex visual data, fixed-layout EPUB or PDF may be appropriate, but test on multiple devices first, as pinch-to-zoom reading is a poor experience for most readers.