If you want a premium experience without paying or risking your PC's security with "free key files," consider these options: 1. Official Ad-Free Tier
If you prefer not to pay for a subscription, you don't need a "license key" to use uTorrent. The of uTorrent Web provides all the core functionality needed to download torrents.
The pursuit of a "free license key" for software that is already free—like uTorrent Web