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(Pocket-lint) - About a year ago Microsoft made Office for iOS free to use on both the iPad and iPhone - and many assumed that would be the case again for Apple's latest iPad, the iPad Pro. But it's not.

The company has confirmed to Ars Technica that Office on the iPad Pro will need an Office 365 subscription in order for you to edit documents, spreadsheets, and the like, whereas you don't need an Office 365 subscription to edit or store stuff in the cloud on an iPad or iPhone.

Office 365 includes several subscription plans. Once you buy one, you'll get varying degrees of access to the Office apps and other productivity and cloud services, such as Lync, Exchange Online, OneDrive, and Skype minutes. Plans start at $6.99 a month and go up from there.

The basic "Personal" tier, for instance, comes with the full Office 2016 experience for PC or Mac, a copy of Offie Mobile for an Android tablet, iPad, and one smartphone. It also comes with 1TB of OneDrive, 60 monthly Skype minutes, and access to the latest Office apps and updates.

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Go here to see a comparison of all the plans. Keep in mind Microsoft has a rule of thumb: any tablet larger than 10.1-inches requires an Office 365 subscription to edit documents using Office Mobile. The company has the same rule for its Windows 10 Office Mobile apps and Android versions.

So, with that in mind, you can understand why Office is free on iOS devices, including both iPads and iPhones. The current iPad models don't go beyond 9.7-inches, which is under Microsoft's 10.1-inch rule, obviously, but the 12.9-inch display of Apple's iPad Pro is just too big.

Microsoft hasn't clarified how it'll limit use of Microsoft Office for iPad Pro. All we know is that you'll need to at least buy an Office 365 Personal subscription for $6.99 a month (or $69.99 a year) if you want to edit documents.

READ: Hands-on: Microsoft Office for iPad apps review‏

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Writing by Elyse Betters. Originally published on 26 September 2015.