Steven has several computers with Windows 7 SP1 and Office 2010. He wants to know if he can buy a Windows 8.1 retail key and then downgrade to Windows 7 for another computer. Leo says no. He'll have to use Windows 8.1. If his computer has an OEM copy of Windows, then he should go to his PC maker and tell them he'd like to buy Windows disks for his computer. They should give him a license for Windows 7. He could also just wait. This summer, Windows 10 will be free to everyone running Windows 7 and above. Then he won't have to deal with it.
Another option is to buy a Windows 7 OEM DVD from NewEgg. They are designed for system integrators, but they're available to anyone now. It costs around $150. That's how he can get an official Windows 7 license key. But he shouldn't delay too long -- Microsoft stopped shipping Windows 7 last October. Amazon may have them too.