.IBOOKS File Extension
What is an IBOOKS file?
Digital book created for the macOS and iOS devices; saved in the ePub 3 format with a few proprietary Apple-specific additions; may include text, images, videos, 3D objects, presentations, and other media; supports user interaction through multi-touch gestures.
iBooks are created with iBooks Author, a free book design and publishing program developed by Apple. They can be exported in the iBooks format, as plain text documents, or as .PDF files. Completed iBooks may also be published to the iBookstore using iTunes Producer. Once an iBook has been published on iTunes, it can be downloaded directly to an iPad. Downloaded iBooks are saved in the following directory:
NOTE: IBOOKS files are saved in the "iBooks 2" format. This file format, which was introduced by Apple on January 19, 2012, is designed for educational textbooks, but can be used for creating any type of digital book.