Each legitimate license is unique, tied to a specific user, and provided only upon purchase from Nikon or an authorized reseller.
If you own a Nikon camera made after 2015, use Nikon NX Tether (free). If you own an older DSLR, use digiCamControl (free). If you are a professional making money from tethering, invest in Capture One (paid).
– Some online stores, including the Nikon Direct shop in Japan, sell a “product key” download. In this case, you first download the trial version from Nikon’s website and then activate it with the key you bought.