Book: The Sacred Books Of The East by Friedrich Max MullerThis Elibron Classics book is a facsimile reprint of a 1879 edition by the Clarendon Press, Oxford. For one interested in a scholarly Commentary for the Avesta, as well as the most recent Complete Translation , this series by James Darmesteter I have found to be the best. Mazdeism (also known as Zoroastrianism), in particular, reveals a great deal about the formative Influences of the Abrahamic religions, as well as Hinduism, from which Buddhism also later developed. It's a bit costly to buy these three volumes of the Avesta, but it is certainly a worthwhile investment.
Books in PDF format to read:Alice Hoffman - The Book Of The Sagas
Lady Galadriel - The New Book Of The Law
Friedrich Max Muller - The Sacred Books Of The East