A family of Microsoft word processing software products for creating web, email, and print documents.
Do you need to stack Windows subscription or Office subscription?
If this is Office subscription, it is only 1 subscription per account. "You can only have one active Office 365 subscription plan per Microsoft account — that’s the email and password you use to install Office
If you add the same Office 365 subscription plan to your Microsoft account, you’ll still have the same subscription benefits as before — but we’ll extend your current subscription for up to 5 years. If you use an Office 365 Personal product key and you currently have an Office 365 Home subscription you'll be offered a choice to stay with the plan you currently have or be switched to Office 365 Personal."
There are further details about this if you add another subscription to your Microsoft account -