EPUB or .epub is mainly a file extension that is used to save eBooks and other types of content. This is one of the most popular eBook formats that can contain words, images, tables of content, stylesheets, metadata details, fonts, and so on. EPUB format is as popular as this file type can responsively adjust in any screen size. Besides they are now supported in most of the hardware that offers eBook reading functions such as Kobo, Barnes & Noble Nook, etc. For desktop and android users, they need to download and install dedicated software to open EPUB files. Here also mentions that you can’t read the EPUB file in kindle as it can’t read it natively.