# What is an EPUB?

EPUB is the open standard file format for ebooks: a zipped package of the book's text, images and styles that a reading app reflows to fit any screen and type size. Chapbook exports EPUB 3, the current version of the standard.

Updated 29 October 2026. Web page: https://chapbook.ink/glossary/epub/

## What is inside one

An EPUB is a ZIP file with a fixed structure: the chapters as XHTML, a stylesheet, the images, the fonts if it carries any, and a package file that lists them in reading order with the book's title, author and language. A navigation document gives reading apps the table of contents.

Because the text is not fixed to pages, the reading app lays it out on the fly. The reader picks the type size and the screen decides the line length, which is why an EPUB reads well on a phone where a PDF page would need zooming.

## EPUB or PDF?

They do different jobs. A PDF is the book exactly as typeset, with the same pages everywhere, which suits a designed guide and anything meant to be printed. An EPUB gives up fixed pages for text that fits any screen, which suits reading apps and ebook stores.

## Chapbook's EPUB

On a paid plan, Chapbook exports every book as both. The EPUB 3 is reflowable, with a navigable table of contents, and the pipeline that builds it is validated against EPUBCheck, the standard's own conformance checker. The sample on this page has its EPUB beside the PDF for download.

## Made with Chapbook: The Pricing Playbook

The Pricing Playbook: How founders set a price they can defend, by Jane Founder. Nonfiction book, 9,862 words, 43 pages. A sample generated from one brief and exported unedited; it is not a customer's book. Read every page: https://chapbook.ink/examples/nonfiction/

The brief:

> A repeatable method for pricing software: customer interviews, a value metric, tiering, and setting numbers you can defend. Promise: A repeatable method for setting a price you can defend to customers, investors and yourself, validated by ten customer interviews in a week. Reader: A founder who priced by guessing or by copying a competitor and now has to defend or change the number. Voice: Direct second person with occasional first person; worked examples with fictional companies; tables where they clarify; no invented statistics or named studies: reason from mechanics and examples.

The outline the planner proposed:

1. Introduction (620 words)
2. Why Guessing Fails (1,014 words)
3. What You Are Actually Selling (1,004 words)
4. Interview Ten Customers (1,088 words)
5. Choose the Value Metric (979 words)
6. Draft Three Tiers (1,076 words)
7. Set the Numbers (1,130 words)
8. Say the Price Out Loud (1,063 words)
9. Revisit Every Quarter (994 words)
10. Conclusion (384 words)
11. Appendix: The Interview Script (475 words)

## Questions

### What is the difference between EPUB and PDF?

An EPUB reflows its text to fit the reader's screen and chosen type size; a PDF keeps fixed pages, exactly as typeset.

### Which should I use for a lead magnet?

A PDF suits most lead magnets, because it keeps the designed layout and opens on any device. Offer the EPUB as well for readers who read on an e-reader.