EPUB File Format (.epub): What It Is and How to Open It

EPUB at a glance#

Full name	Electronic Publication
File extension	.epub
Category	Documents
Developer	International Digital Publishing Forum
First released	2007
MIME types	application/epub+zip
Compression	Lossless
Specification	EPUB 3.3 (W3C Recommendation)
FileFlip support	FileFlip reads and writes this format

What a .epub file can hold#

These are the things a EPUB file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Embedded metadata	Yes
Multiple images or pages	Yes
Selectable text	Yes
Audio	Yes
Video	Yes
Chapters	Yes
Encryption	Yes

Strengths and limitations of EPUB#

What EPUB does well

Reflows text to fit any screen size instead of pinning it to a fixed page
Opens natively in almost every e-reader app and device except Kindle
Carries a table of contents, cover image and Dublin Core metadata inside the file itself
EPUB 3 can embed audio, video and MathML on top of plain text

Where EPUB falls short

Kindle devices and apps do not open EPUB directly; Amazon converts it on import instead
EPUB 2 and EPUB 3 readers do not always agree on how newer layout features render
A publisher-applied DRM scheme like Adobe ADEPT locks the file to specific reading apps
Fixed-layout EPUB exists for comics and children's books but gives up the reflow that makes EPUB useful elsewhere

Use EPUB for any ebook meant to reflow to the reader's screen and open on Kobo, Apple Books, Google Play Books or Adobe Digital Editions.

Convert away from EPUB when a Kindle needs the file in KFX or AZW3, or when the fixed page layout of a PDF matters more than reflow.

How to open a .epub file#

A .epub file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts EPUB into a format your machine already opens, and it does it in the browser tab rather than on a server.

Platform	Programs that open it
Windows	Calibre, SumatraPDF, Adobe Digital Editions
macOS	Apple Books, Calibre, Adobe Digital Editions
Linux	Calibre, Okular, FBReader
iOS	Apple Books, Kobo, Google Play Books
Android	Google Play Books, Kobo, Moon+ Reader
Web	FileFlip

EPUB questions people ask#

What is an EPUB file?

An EPUB file is an ebook packaged as a ZIP archive of XHTML pages, CSS and images, which is why the text reflows to fit whatever device opens it rather than staying pinned to a fixed page. It is the open ebook standard, maintained by the W3C, and every major reading app supports it except Kindle.

Why won't my Kindle open an EPUB file?

Kindle devices and the Kindle app do not read EPUB natively. Amazon's Send to Kindle service accepts an EPUB upload but converts it internally to KFX before it reaches the device, so the file itself still needs to go through that conversion rather than being copied over as-is.

What is the difference between EPUB 2 and EPUB 3?

EPUB 2, finalized in 2010, covers text-centric books built from XHTML and CSS. EPUB 3, released in 2011, added fixed-layout pages for comics and picture books, MathML for equations, and support for embedded audio and video, so a modern EPUB file can do things a 2010-era reading app was never built to handle.

Can I remove DRM from an EPUB file to convert it?

No converter can remove DRM from an EPUB file. When a book is protected with Adobe's ADEPT scheme or a retailer's own encryption, the actual page content is encrypted inside the archive, and a conversion tool that receives the file will fail or produce a broken output rather than strip the protection.

Do EPUB files store images inside them?

Yes, an EPUB file bundles every image it uses inside its own ZIP archive alongside the XHTML and CSS, so it never depends on fetching images from the web the way an HTML page can.

Converting EPUB files#

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.

EPUB File Format (.epub)