I have this book in print too, and I bought this so that I could read and reference it on the go. Excellent stuff.
The book is attractive, well laid out and the colours and illustrations used in the book match the theme of DH very well.
This is a brilliant game and well worth the money. As the previous reviewer says, Cthulhu in Space is one way to approach it :)
Obviously it lends itself to all manner of scenario themes, don't imagine it always has to be Chaos Cultists!
I Bought this 12 Jan 2011 and one thing I would point out about this PDF version which annoyed me greatly is that the Errata have not been incorporated in their entirety. The first round of errata which extended to 1.5 pages (approx) have been updated in the version of the PDF, but the Errata was last updated and published on the 23 April 2009 and there are 9 pages of ammendments and clarifactions that haven't been incorporated. Has there really been no opportunity over the last 2 years to produce an up-to-date version of the PDF with all the Errata in?
I have marked it down one mark because of this, otherwise it would have got a 5.