Cant install fonts?

I havent added any fonts to my computer in a long time, so the other day i decided to find some good ones.

Ive installed some before i know you just go to the windows folder and drag the file into the fonts folder.

I tried that and it said “File is currently being used and cannot be replaced, pleas try again when windows if finished with it”

What gives? Ive restarted and everything?