Yes, all you need is a key. When you buy a DVD with a key, its the key that you pay for. You may get a key and a DVD. Just use the key number, you do not have to reinstall or anything. You can save the DVD in case of problems, with the DVD, you can reinstall or make repairs, if ever necessary
Once again to be sure. Buy a key, which may come with a DVD, Just use the key, no need to use the DVd, now.