Originally Posted by Sharkus
If you download the Kobo iOS app it's an .ipa file, this is basically just a zip file, so change the extension from .ipa to .zip, then double-click on it to expand it, and you can have a poke around if you like.
Note that you probably won't be able to view most of the images, well, certainly not in the Preview app. It's something to do with how they are packaged for iOS
Makes you wonder how many other file 'formats' out there are actually just renamed zip files.