Convert OPF to EPUB

A publishing workflow, archive, or reading application may provide an OPF package while the target reader or distribution service requires one .epub file. Conversion packages the OPF, XHTML, stylesheets, images, fonts, and navigation resources into the EPUB container.

What the OPF format is

OPF, normally identified by the .opf extension, is an XML package document used by EPUB production systems. It defines metadata, the resource manifest, and the reading order through elements such as <metadata>, <manifest>, and <spine>.

An OPF file is usually not a complete ebook. It references XHTML or HTML chapters, CSS, images, fonts, cover files, and navigation documents at relative paths. Those files must remain in the locations declared by the manifest. OPF files are used by publishers, ebook authoring applications, Calibre projects, digital libraries, and extracted EPUB packages; they are not normally opened directly in reading software.

What the EPUB format is

EPUB is a ZIP-based ebook container that packages the OPF document with the resources it references. An EPUB must include a root-level mimetype file containing application/epub+zip, a META-INF/container.xml file identifying the package document, and the content files named by that package.

EPUB 2 commonly uses an OPF package and an NCX table of contents. EPUB 3 uses the OPF package with an XHTML navigation document and can support features such as semantic HTML, MathML, media overlays, audio, video, scripting, and fixed layouts, subject to reader support.

EPUB's reflowable layout adapts text to different screen sizes, while one file can carry metadata, navigation, stylesheets, images, and fonts. Apple Books, Kobo, Thorium Reader, Adobe Digital Editions, many Android reading apps, and ebook distribution services support EPUB, although individual feature support differs.

Convert a complete OPF project with Calibre

1. Place the OPF file and every referenced XHTML or HTML file, stylesheet, image, font, cover, and navigation document in the directory structure specified by the manifest. Preserve relative paths and filename capitalization.
2. Install the current desktop release of Calibre from calibre-ebook.com.
3. Run the command-line converter from the project directory:
   ebook-convert book.opf book.epub
4. Alternatively, try the graphical workflow: use Calibre → Add books, select the source, choose Convert books, select EPUB as the output format, and start the conversion. If the graphical importer does not accept the OPF, use ebook-convert.
5. Open the output in the intended reading application and check the chapter order, table of contents, images, links, fonts, cover, and metadata.

Calibre can resolve the OPF manifest, rebuild the EPUB container, normalize metadata, and rewrite incompatible HTML or CSS. It may alter source markup and styling, so retain the original project when exact rendering or source preservation matters. Adobe Digital Editions is a reader, not a general OPF-to-EPUB converter.

Rebuild an EPUB that was extracted

If the OPF came from an extracted EPUB and all package files are still present, conversion through Calibre is unnecessary. Recreate the EPUB ZIP with the original directory structure. The package root must contain mimetype, META-INF/container.xml, the package document named by container.xml, and all manifest resources.

From the package root, create the archive with the mimetype entry first and uncompressed:

zip -X0 ../book.epub mimetype
zip -rX9 ../book.epub META-INF OEBPS

Replace OEBPS with the actual content directory and include every directory referenced by container.xml and the OPF manifest. The mimetype file must contain exactly application/epub+zip, with no additional whitespace, and must be the first ZIP entry. Use an EPUB-aware packaging tool if the operating system's archive utility cannot preserve these requirements.

Validate the EPUB

Run the official EPUBCheck utility against the result:

epubcheck book.epub

EPUBCheck detects malformed package metadata, broken manifest or spine references, invalid navigation, incorrect MIME declarations, and container-structure errors. It cannot restore missing files or correct poor HTML, CSS, typography, or visual layout.

Online converters and compatibility limits

Most online ebook converters accept a single document, not an OPF project with its referenced directory tree. Uploading only the .opf file can produce an incomplete EPUB or omit assets without making the failure obvious. For unpublished manuscripts or licensed content, local Calibre processing avoids sending the source to a third party.

Reputable services such as CloudConvert and Zamzar can be considered only when their current format list explicitly accepts the supplied OPF or a complete package archive and explains how external resources are resolved. They are more appropriate for a packaged ebook or a simple single-file conversion than for a multi-file OPF project. Validate any online result with EPUBCheck and test it in the target reader.

• An OPF cannot provide chapters, images, CSS, fonts, or navigation files that are missing from its manifest references.
• Paths inside EPUB packages are effectively case-sensitive. A reference to Images/Cover.jpg does not reliably resolve images/cover.jpg.
• Calibre may change CSS, HTML, metadata, navigation, and image handling during conversion; compare the output with the source.
• Embedded fonts require valid MIME types and appropriate font licensing. Some readers ignore them or restrict their use.
• JavaScript, fixed layouts, MathML, media overlays, audio, video, and other EPUB 3 features have uneven support. Test on the actual app, device, or distribution validator.