

You can click the small link at the bottom of the installer that says “I don’t have a product key” and proceed through. It will then ask you what edition of Windows you want to install. This is because many PCs have hardware entitlements, so they never got a key.
The only limitation is you can’t customize your desktop/themes and there will be a permeant watermark in the lower right corner asking you to activate.
You can run it unactivated, but it reduces some functionality. The installer has a “I don’t have a product key” option to bypass the key entry screen.