What is a EPUB file?
EPUB — e-book
What is it?
EPUB is the standard format for e-books. Its defining trait: the text is reflowable. It automatically reformats itself based on screen size, font, and font size chosen by the reader — the exact opposite of a PDF, which locks the page in place.
An EPUB file is essentially a small website packed into an archive: XHTML files for the chapters, CSS for styling, a table of contents, and metadata. This is what lets it display just as well on a six-inch e-reader as on a computer screen.
History & origin
The format was standardized in 2007 by the IDPF, the digital publishing consortium, replacing an older exchange format. EPUB 3, released in 2011, added support for audio, video, and non-Latin scripts.
Since 2017, EPUB has been maintained by the W3C, the organization that governs the web — a logical move, since the format relies on web technologies.
Why it is useful
Reading comfort: enlarging the font doesn't just zoom in, it completely reflows the page. For a long text read on screen, the difference with a PDF is striking.
It includes a navigable table of contents, proper metadata (author, publisher, ISBN), and takes up very little space. Every e-reader can open it — even Kindles, which don't support it natively but convert it upon receipt.
Limits & drawbacks
It's poorly suited to fixed layouts: a comic book, an illustrated textbook, or a report with columns will look distorted. Flowing text doesn't work with a page designed down to the millimeter.
The final rendering depends on the e-reader and the reader's settings: you have no control over exactly what they'll see. Some files are also locked behind digital rights management that prevents reading outside the intended app.
Practical tips
EPUB is the right choice for a novel, an essay, documentation — anything made of continuous text. For a document where layout matters, convert it to PDF instead.
Conversely, if you have a long text-based PDF you want to read comfortably on an e-reader or phone, converting it to EPUB changes everything: the text becomes reflowable again instead of forcing you to zoom in on an A4 page.
Convert your EPUB in seconds, on our secure servers in France.
Convert a EPUB