It is an ePub file and can be opened with most readers on mobile devices, and also on Macs and Pcs.
Google Play Books
Universal Book Reader
You can also use the browser extension:
-EPUBReader for Chrome and Firefox
-Readium for Chrome
You should be able to download one of these options from your usual app store.
If you have any problems opening the file please ask for assistance at email@example.com