I don't know about India, but you most certainly can use a Nook without a US address or credit card! You do not need to root it to do that. I use my Nook in Sweden, right out of the box.
You can register it with any e-mail address and you you don't have to give an address or credit card details just to register it and use it.
You won't be able to buy content from Barnes and Noble without giving a US adress and some other "fixes", but sideloading work perfectly!
I'm not sure a Nook STR would be the best choice for PDF reading though, but that's another story...