Connecting a desktop copy of Office to a Microsoft 365 tenant, so that Word, Excel, and Outlook activate against the organization's subscription rather than asking for a separate license key, is a normal step when setting up a new machine. The exact process below applies to Microsoft 365 Apps, the current, continuously updated version of Office that comes with most Microsoft 365 business plans. If a machine still has an older, permanently licensed version like Office 2016 installed, that specific edition has reached the end of Microsoft's support lifecycle, and the right move is to replace it with Microsoft 365 Apps rather than reconnect an outdated version.
Signing in to activate
Open any Office app, such as Word, and you will be prompted to sign in. Use the work or school account tied to the Microsoft 365 subscription, not a personal Microsoft account. Once signed in, Office activates automatically against that tenant's license, and the same sign in carries across every other Office app on the machine.
If it does not prompt automatically
Open any Office app, go to File, then Account, and check the sign in status shown there. If it shows as not signed in or shows a different account than expected, select Sign in or Switch account and enter the correct work or school credentials.
If the license shows as unlicensed after signing in
This usually means the signed in user does not actually have a Microsoft 365 license assigned in the admin center, rather than a problem with Office itself. Confirm in the Microsoft 365 admin center that the user has a license that includes Microsoft 365 Apps assigned to their account, since a valid sign in alone does not activate Office if no license is behind it.
Deploying Office across many machines at once
For more than a handful of devices, installing and activating Office one machine at a time does not scale well. The Office Deployment Tool, combined with Intune or a similar device management platform, lets you push a consistent, pre-configured install to every machine automatically, which is worth setting up before a wider device rollout rather than after.
If you are still running an outdated, permanently licensed version of Office anywhere in your organization, or want device setup properly automated instead of handled one machine at a time, our managed IT services team can help. Get in touch if that is where you are at.