Please visit this helpful article by Andre Da Costa on how to purchase a Windows 7 product
If you upgraded to Windows 10 for free from Windows 7, then you should have a digital license instead of a product key. Learn more about activation in Windows 10. The product key is in the confirmation email you received after purchasing it or it may be distributed as a digital license if you bought Windows 10, in which
The product key is found on a label or card inside the box that Windows came in.
The Windows 7 product key is a 25-character code that's used to activate Windows and where you find it depends on how you got your copy of Windows: