The iPad Pro, with its optional stylus and keyboard-cover, should be a fine machine to run Microsoft's Office apps for iOS.

And it probably will be, but there's a catch. The Office apps on the current iPads offer both viewing and editing documents for free. A handful of features require Office 365 subscriptions, available as in-app purchases, but the core editing capabilities are all zero cost.

Install those same apps on the iPad Pro once it arrives in November, however, and all those editing features will go away. Office on the iPad Pro will require an Office 365 subscription for any and all editing.

That's because Microsoft defines a 10.1 inch cutoff. Anything below 10.1 inches is a "true mobile device" and as such qualifies for free access to the core editing capabilities. But above that threshold and it's not a "true mobile device" any longer, it's something else entirely, and it will need an Office 365 subscription as a result.

Vexingly, while the EULA for the Android apps describes this cut-off, and the different screen-dependent licensing conditions, the iOS app license does not. So for Android, Microsoft writes:

PLEASE NOTE: If you only use the application on devices with a screen less than or equal to 10.1 inches to view documents and perform core editing features, see Section C below. If you use the application on devices with a screen size less than or equal to 10.1 inches or devices with a screen size greater than 10.1 inches to unlock premium editing features in addition to the core features, see Sections A and B below to determine which section applies to your use of the application. If you are not a Microsoft Office 365 subscriber entitled to the rights under Sections A or B, see Section C below and note your use is limited to viewing and printing features.

The equivalent text for iOS, however, reads:

PLEASE NOTE: If you only use the application to view documents and perform core editing features, see Section C below. If you use the application to unlock premium editing features in addition to the core features, see Sections A and B below to determine which section applies to your use of the application.

Similarly, the application description for Android includes this restriction:

The free Microsoft Word app provides a core experience for viewing, creating and editing docs on devices with a screen size of 10.1 inches or smaller. You can unlock the full Word experience with an Office 365 subscription.

As does the one for the Windows Store Metro apps:

This version of Word is built for phones and tablets (with a screen size of 10.1 inches or smaller). On those devices you can view, create, and edit Word documents for free. You need a qualifying Office 365 subscription to use advanced features. Learn more at www.office.com/information. On larger tablets, laptops, and desktops, you can view documents for free. A qualifying Office 365 subscription is required to create and edit documents. Office 365 also includes the latest desktop versions of Word, Excel, PowerPoint, OneNote and Outlook - recommended for use on desktops and laptops.

In spite of the lack of relevant licensing or descriptive text, Microsoft confirms to us that when run on the iPad Pro, the Office apps will detect the larger screen and lock their editing capabilities until an active subscription is provided require an active subscription. Perhaps the extra wording will be added in time for the iPad Pro's launch. Either way, current users planning to upgrade to the bigger device are going to have to pay for a subscription if they're going to want to keep editing their documents. Apple's already expensive premium tablet will be made that little bit more expensive.

Update: Prior to publication, we contacted Microsoft about this licensing situation, and company representatives confirmed both the subscription requirement, and that the software would in some way enforce the lock-out on the iPad Pro. Since publication, the company gave us a clarification that while the licensing and subscription requirement is accurate, the user experience has not been finalized or publicly revealed, and that it is too early to say precisely what will happen, if anything, when users try to run the software on the iPad Pro.