wmic path SoftwareLicensingService get OA3xOriginalProductKey to check if a key is stored in your system's BIOS. Registry Extraction : Third-party tools like Belarc Advisor
For modern subscription versions (Office 365 / Click-to-Run), the activation state is stored in files located in: %localappdata%\Microsoft\Office\16.0\Licenses Index Of Ms Office 2016 Product Key
Using an index of MS Office 2016 product key can have several benefits, including: they may be blocked
Keys found in public indexes rarely work long-term; they may be blocked, already used, or tied to different licenses/regions. Support and updates from Microsoft won’t be available for illicit activations. Index Of Ms Office 2016 Product Key