The document discusses digital books, including their definition as digital forms of printed books that can contain text, images, audio, and video and be read on devices like computers, tablets, and smartphones. It covers the types, formats, functions and goals of digital books, as well as the applications used to create and read them. The main points are that ePub is one of the most popular digital book formats as it is open, supported by many reading applications and devices, and allows reflowable text and inclusion of multimedia; and that the software Sigil is an open-source ePub editor that allows viewing and editing the code and previewing