Kepub is a term used to describe the eBook format designed for Kobobooks.
The Kobo company has developed their own variation on standard ePubs. Kobo eReaders have an SQLite database that helps them read and manage books that come from their bookstore or another bookstore that has adopted their format. In some cases the books downloaded from their web store will be stored directly in this database and in other cases the books will be stored separately but will be referenced and managed from the database.
The application used to read these eBooks is call Nickel. It is the only reading application on a Kobo Device and can read ePub as well as PDF and CBZ formats. It is capable of working with Adobe DRM. It is also available as Kobo eReading Apps for a wide variety of platforms. While the application can read both kepub and ePub there are differences. For example the kepub can now be coded to meet the ePub 3 standard.
Kobobooks stores can also sell ePub books which can be read on any device that supports ePub. The user will need to ensure which formats are available for a particular book. Regular ePub support uses Adobe's RMSDK engine while Kobo ePub support uses NetFront's ACCESS engine.
Note that a kepub formatted book needs the extension to be .kepub.epub, that is two extensions. Otherwise it will not recognize the book as different from a normal epub.
 kepub folder
If you attach a Kobo reading device to your computer via USB you will find that it mounts the reader's internal memory as an external disk drive on the computer. You can examine the contents of this area and will find a .kobo folder. (If your computer runs Linux, you may need to use the "view hidden files" option in your preferred file manager to see the folder because its name starts with a period.)
Inside the .kobo folder you will find the SQLite database and a second folder called kepub. It holds a number of files with long numbered names and no extension, each of which contains one of the books on your device. If you copy one of them to your computer and add .zip to the end of the name so you can open it, you will find that it is really an ePub file. Most of the contents are encrypted with DRM, but some files are in plain text such as the OPF file and the CSS file. Beginning with version 1.9 of Kobo's operating system, the Kepub format became the primary type of ePub on their devices.
On a PC running Windows, you will find this same information stored at \Documents and Settings\Your Name\Local Settings\Applications Data\Kobo\Kobo Desktop Edition (\Users\Your Name etc. on Vista and Windows 7).
The Kobo.sqlite database is the heart of the Kobo system. SQLite is a standard database and you can use readily available tools to look at its content. However, the actual structure is not documented and any changes could corrupt the database so are not recommended.
 Kepub compared to ePub
The kepub format is compatible with ePub leading some to theorize that they could just change the extension to .kepub.epub to make a Kepub from an ePub. However there are some differences. In a kepub, each sentence is wrapped in a span. This is assigned a unique id. The location system uses these ids. If you just change the extension, when you close and reopen a book, you will always be taken to the start of the chapter you were in. And any annotations stored will not be redisplayed in the book. A conversion of ePub to kepub will add the spans to the epubs. There are also some extra divs and CSS that the kepub ereader expects which helps with the way it does the formatting. The DRM system is also different for eBooks using DRM. Kepub also supports ePub 3 formatting which is still not supported for ePub.
Kepub files use a proprietary DRM scheme, sometimes called "kdrm" due to its characteristic xml tags in the rights.xml file. While many kdrm-protected kepub ebooks are also available for download as regular epubs with ubiquitous Adobe DRM, this is not always the case, restricting the use of these ebooks to Kobo devices and reading applications. Tools to remove this DRM scheme have recently been developed.
Extras features are available for eBooks being managed by the Kobo database. Some are restricted to only purchased DRM eBooks. Some are no longer applicable to latest firmware.
- highlighting of words in the document.
- multiple bookmarks of pages in the document.
- dictionary lookup of a selected word in the document.
- being able to add annotation to a highlighted word.
Comparison of Kepub and ePub with both on a Kobo device.
Positive: KePub (sideloaded):
- Quicker to respond to page turn gestures (especially tap gesture)
- Faster text selection (e.g. when highlighting large areas of text)
- Support for footnote previews
- Can double-tap to zoom images
- Shows number of minutes of reading left until end of chapter
- Shows title of ebook in the header (negative for some people)
- support for ePub 3.
Positives for standard ePub on a Kobo device:
- Better hyphenation (kepub reader can hyphenate words in the wrong place if they have trailing punctuation)
- Full justification works properly (kepub reader doesn't properly justify some lines that contain certain common characters such as ellipsis and emdash)
- Better support for embedded fonts
- Full-screen mode works without fonts being cut off
- Better word spacing when using full justification
(Apart from the last, all of these ePub advantages are due to bugs in the KePub reader.)