A professor has offered to send me a hard copy of his new book. Would it be rude to ask for a PDF file instead? While working my way through one textbook, I spotted several errors, TeXed them up and emailed to the author of the textbook. He thanked me and asked for my physical address so he could send me a copy of his new textbook (a more advanced one). I was planning to work though his new textbook anyway, since it matches my interests. Yet I'd much prefer a PDF file and not a hard copy. Would it be rude to ask if he could send me a PDF file instead? I don't want to come over as ungrateful, yet I'd make much more use of it if I had a PDF file.

Definitely of relevance here:


He certainly does have a PDF file of the new book since the publisher offers PDF as one of the options (hardcover, softcover, and PDF file),
The PDF file in question can not be 'freely' found on the Internet (although its previous edition can).
It is a question of framing. Frame it as something that is good for him, not just for you. I'd write something along the lines of: 


  Thank you very much for your kind offer. I'm indeed  very interested in the subject of book X. It probably is easier and cheaper for you if you just send me a PDF, and as I am someone who reads mostly on a screen anyway, I would be equally happy with an electronic version.


(And then you might or might not mention your postal address anyway, but in any case stress again that it is up to him to decide.)

In fact, I have had such situations before (people asking me for a copy of my dissertation [which I would have send them for free in print], but who also mailed that they preferred a PDF).