Open an ePub file using a Windows utility such as ePub Reader for Windows; many of these ePub applications are free or have free trials available before purchase. Digital books are arguably the most common type of ePub publications, and they require e-book software especially designed to open and read them.
Calibre is a free and open source software that can open just about any ePub file format with no problem. Moreover, another strength is that it's a fairly platform-agnostic software: It can be used on Windows, OS X and Linux. The software can be downloaded from its website.
For Apple fans, the technology giant has iBooks, which can also open and read ePub files. It's a built-in application on iOS 8, and for pre-iOS 8 users, the app is also available for download from the App Store.
For Android fans, the Aldiko Book Reader and Universal Book Reader are two applications that fully support ePub files. Aldiko has a version that enables users to add notes and use a highlighting feature; the app can be downloaded from its website or from Google Play. The Universal Book Reader enables page flipping, among other capabilities, and can be downloaded from Google Play or directly from its website.