There are several PDF apps which could read books in PDF form, also Nokia Reading in the store along with the Kindle app all in the Microsoft store. You could also read things via the browser or save books to your skydrive account and access them on your Lumia.
If I have helped at all, a click on the White Star is always appreciated :
you can also help others by marking 'accept as solution'
Press the 'Accept As Solution' icon if I have solved your problem, click on the Star Icon below if my advice has helped you!