.epub File Extension
.epub ebook is, which apps open it, how Poly supports it, and when PDF or another ebook format may work better. File extension details for .epub
Full Support| File type | EPUB electronic publication |
|---|---|
| MIME type | |
| Encoding | Binary OCF ZIP container with XHTML, CSS, XML metadata, and media assets |
| Operating systems | Windows, macOS, Linux, iOS, Android |
| Opens with | Apple Books, calibre, Adobe Digital Editions, Kobo readers |
| Poly support | Yes. Poly provides rich document support for EPUB ebooks. |
| Indexed by Poly | Yes. Poly indexes readable text, OCR results, and page-level visual similarity. |
| Preview in Poly | Yes. EPUB files open as a paginated document preview. |
| Poly agent | Yes. The Poly agent can read and reason about supported book text and images. |
What kind of file is an .epub?
An .epub file is an electronic publication packaged in EPUB's Open Container Format. It normally uses the application/epub+zip MIME type. Inside the container are the book's XHTML or SVG content, CSS, images, fonts, navigation, metadata, and reading order.1
Most EPUB books are reflowable, so a reading app can repaginate the text when you change the screen size, font, spacing, or theme. The standard also supports fixed-layout publications when exact page geometry matters.
An EPUB begins like a ZIP file with 50 4B 03 04, but those four bytes are not enough to identify it. A conforming file places an uncompressed entry named mimetype first, containing exactly application/epub+zip. It also includes META-INF/container.xml, which points the reader to the publication package.12
book.zip to book.epub does not create an ebook. Renaming an EPUB to .zip can help you inspect a copy, but repackaging it incorrectly may make it unreadable.How do I open an .epub on my computer?
- On macOS, iPhone, and iPad, import the file into Apple Books. Apple documents importing EPUB books obtained outside its store.3
- On Windows, macOS, and Linux, calibre provides an EPUB viewer with search, bookmarks, read-aloud, paged reading, and continuous flow.4
- On Android or a dedicated ereader, use a compatible reading app such as Kobo or the app recommended by the ebook provider.
A web browser does not usually open EPUB files by itself. Browser-based readers and extensions add the reading system. Store or library books protected by digital rights management may require an authorized app and account.
Poly support for .epub
Poly gives EPUB ebooks a first-page thumbnail, a paginated in-app preview, full-text search, OCR when needed, and page-level visual search. The Poly agent can use supported text and images to summarize a chapter, answer questions, or help locate a passage.
The preview presents a stable paginated view rather than a native reflowable reading experience. Font controls, scripted interaction, media overlays, and pagination from another reader may not carry over. Encrypted, DRM-protected, damaged, or unsupported publications can have limited processing.
History of .epub
EPUB grew from the Open eBook Publication Structure. Its original standards organization, the International Digital Publishing Forum, introduced the EPUB name with EPUB 2.0 in 2007. EPUB 3.0 followed in 2011 with richer web technologies, global-language support, media overlays, scripting, and stronger accessibility features. EPUB 3.3 later became a W3C Recommendation.5
The .epub suffix identifies the packaged publication, while application/epub+zip identifies its registered media type. The format remains open, standardized, and widely used for ebook distribution.2
Working with .epub and alternatives
| Format | Best fit | Main tradeoff |
|---|---|---|
| EPUB | Responsive books and accessible digital reading | Rendering and pagination can vary by reader |
| Printing and exact page geometry | Text usually does not reflow to small screens | |
| AZW3 | Established Kindle workflows | Proprietary and less portable |
Use calibre to convert an unprotected EPUB when another device or workflow requires PDF, DOCX, or a reader-specific format. Conversion can change fonts, image placement, navigation, footnotes, and page breaks, so inspect the result. It cannot remove DRM lawfully or recover features that the destination cannot represent.
Validate edited or repackaged books with EPUBCheck. Also treat unfamiliar EPUB files as untrusted content because they can contain scripts, external links, remote resources, forms, and embedded media.67
Footnotes
- World Wide Web Consortium. EPUB 3.3. See the publication model and Open Container Format requirements. ↩ ↩2
- Internet Assigned Numbers Authority. application/epub+zip Media Type Registration. ↩ ↩2
- Apple. Import Books, Audiobooks, or PDFs in Books on Mac. ↩
- calibre. The E-book Viewer. ↩
- World Wide Web Consortium. EPUB Revision History. ↩
- World Wide Web Consortium and DAISY Consortium. EPUBCheck. ↩
- World Wide Web Consortium. EPUB Reading Systems 3.3: Security and Privacy. ↩