OPF File

What are OPF files and how to open them

Are you having problems opening an OPF file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your OPF files.

What is an OPF file?

OPF files have multiple uses, and EPUB Package Document Metadata is one of them. Read more about the other uses further down the page.

EPUB Package Document Metadata

EPUB Package Document Metadata (.OPF) files are parts of EPUB eBooks. They are XML documents created when an EPUB is assembled. An EPUB-reading program or tool writes this file, while eBook readers and cataloging software read it to locate and present the book's metadata, structure, and reading order.

Inside the OPF file are several sections. The metadata section gives details like title, author, language, unique identifier (such as ISBN), and the last modified date. The manifest section lists every file in the publication (text, images, stylesheets, fonts, etc.). The spine section specifies the linear order in which the reader should display content. For older EPUB versions, a guide or NCX file provided table of content data; newer EPUBs use an XHTML navigation document instead.

This XML-based file uses a root element (<package>) with attributes including version (to show EPUB spec version like 3.0 or later) and unique-identifier (referring to a dc:identifier element). Mandatory child elements under <package> include <metadata> (at least title, identifier, and language plus modified date), <manifest>, and <spine>. Optional elements depend on EPUB version. Its MIME media type is application/oebps-package+xml.

Technically the file begins with the XML declaration (<?xml version="1.0" …?>), includes XML namespaces such as xmlns="http://www.idpf.org/2007/opf", and contains keywords like UNIQUE-IDENTIFIER, METADATA, MANIFEST, SPINE, LANGUAGE, TITLE, CREATOR, HREF and media type attributes.

How to open OPF files

We have identified one OPF opener that is compatible with this specific type of OPF file.

Programs that open EPUB Package Document Metadata files

Last updated: August 10, 2026

All known file formats using extension .OPF

While EPUB Package Document Metadata is a popular type of OPF-file, we know of 6 different uses of the .OPF file extension. Different software may use files with the same extension for different types of data.

Obsidium Project File

We know that one OPF format is Obsidium Project File. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

While we have not verified the apps ourselves yet, our users have suggested ten different OPF openers which you will find listed below.

OEB Package Format EBook

We know that one OPF format is OEB Package Format EBook. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

OmniPass Encrypted

We know that one OPF format is OmniPass Encrypted. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Open Packaging Format E-book Data

OPF stands for Open Packaging Format. The Open Packaging Format is a standard that is a part of the EPUB eBook specification. The OPF files store information for an associated eBook, including the title of the eBook, the eBook language, creator, reading order, and book ID. The OPF file is included in the EPUB archive to specify the metadata of the associated eBook. The OPF files are saved in XML format.

Outforce Packed Content

We know that one OPF format is Outforce Packed Content. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of OPF files. Remember, different programs may use OPF files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about OPF file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.