After a lot of time and a lot of frustration with information from different sources, with the help of the UBNT Community I managed to configure my network to use Sky working with Unifi hardware.
EPUB format works on any device with an EPUB reader; it allows interactive content such as video, image galleries and widgets and text re-flows based on screen size.
Firefox has a free EPUB reader extension and Chrome has a free EPUB reader extension.
If you are an Apple user the native Books app will open ePub beautifully.
PDF version is much more limited and provides text, images and web links.