So the wife bought a win10 laptop. Came from staples with Win10 on it. Is it possible to free downgrade to Win8.1 since she has software that won't work with Win10? The
Downgrade rights vary. Reading material: Downgrade rights for Windows 10 – licensing how-to
That's... not free.
It's possible to downgrade if you upgraded from 7/8... but not from a fresh W10 installation.
It might be possible to run the program in W8 compatibility mode, but you may well be looking at getting a copy of Windows 8.