One of the challenges Microsoft faces is that some people haven't upgraded their Office suite for several years, despite the company releasing new versions.

People pay a relatively large sum for access to apps like Word and Excel, and once they have the functionality they need, there's little incentive to upgrade. It makes sense from a consumer standpoint, but it means Microsoft isn't making as much money as it could from the widespread use of Office.

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That could be the impetus behind a promotion Microsoft announced Tuesday: People who have Windows 10 on their computer but are still running Office 2010 or earlier can now get a one-year Office 365 Personal subscription for $35. That's half the price Microsoft usually charges for the Personal package, which lets users install its productivity suite on one tablet, one computer and one phone.

It comes the same day that Microsoft launched Office 2016, the latest update to its productivity suite. The update includes a variety of new features like integration with Bing search and a "Tell Me" search box that helps people find functionality inside the Office apps without having to comb through a maze of menus.

What's more, the update enhances collaboration between Office users. One of the marquee features is real-time co-authoring in Word's desktop app, which lets multiple people work on the same document at the same time and see the edits of other users in real time. The success of that feature relies on people using Office 2016, which means it's in Microsoft's interest to get more people onto Office 365.

Of course, the promotion is only good for a year -- users have to pay the full $70 for an Office 365 Personal subscription once their promotional period is up. It's not clear when the deal will end, either, though it seems unlikely that Microsoft will keep it around forever.

It's not clear how many new Office 365 users Microsoft will manage to snag with the promotion, but it could help boost the number of users who pay for a subscription, and therefore keep feeding Microsoft's annual revenue, rather than forking over a lump sum when they feel like upgrading.