If you already own the software but need to re-install it, you can typically find your 25-digit product key in the following places:
If you registered your software, you can often retrieve your key by signing into your account on the Nikon Service & Support website under "My Stuff" or "My Camera Bag".
: Once you find and save your product key, consider backing it up. This could save you from future headaches if you need to reinstall the software.