Popular Woodworking operates its digital service via a third party called Zinio. They're not the best, in particular you're limited to printing individual pages rather than printing off a full article from pages X through to Y, and downloading isn't permitted. I believe that if you finish your subscription your purchased magazines remain accessible, but I don't know what happens if Zinio themselves go under?
Fine Woodworking seem to have a better digital model, at least as far as printing and downloads are concerned, their search facility seems better too, but they have hard locked video advertising which can get a bit intrusive.