If you have a big storage device you can just partition it and have dual boot, or if you need to use windows stuff you can always virtualize it with Virtualbox for example.
Answering you question, you just need to download the windows iso and use MAS(google it) to activate windows/office permanently. But anyway nowadays isn't required to activate windows unless you want to change how your desktop looks.
I use it, it works pretty good tbh.