Both PDF and EPUB versions are included in your downloaded zip file.
Unzip the file and you should see both an .epub file and an .opf file.
EPUB files can be opened in most e-book readers, including the B&N Nook, Kobo eReader, and Apple’s iBooks app. EPUB files have to be converted before they’re usable on the Amazon Kindle.
EPUB files can also be opened on a computer with several free programs, such as Calibre, Adobe Digital Editions, iBooks, EPUB File Reader, Stanza Desktop, Okular, and Sumatra PDF. Microsoft Edge, the default browser in Windows 10, features out-of-the-box support for reading EPUB files.
PDF files can be opened on any computer using Adobe Acrobat and most mobile devices.