James Vincent, writing for The Verge:
Apple wants the iPad Pro to replace Windows, and to convince customers it's bringing in a familiar face or two: Microsoft's Office Suite. As part of the ordering process for the new iPad Pro, buyers are given the option of adding a subscription for Office 365 — the only non-Apple accessory to appear in the order form. Office 365 bundles in the mobile apps and full Mac versions of a number of old standbys, including Word, Excel, PowerPoint, and OneNote. (You can also choose between the Home, Personal, and University tiers, each of which offers different features.)
The Microsoft Office apps for iOS are easily some of the best apps available, particularly for the iPad. Whilst they aren't yet at feature parity with their Windows and Mac counterparts, they are remarkably close in many respects. I've been using the Word, OneNote and Excel iPad apps extensively in the recent weeks, and I have been really happy with how they work.
It is worth noting that Microsoft Office is actually free to use on the 9.7" iPad Pro, but requires an Office 365 subscription if you want to edit documents on the 12.9" iPad Pro. This disparity is because of Microsoft's rather odd policy in which Office is free to use on any device with a display smaller than 10.1" - but for devices with a larger screen, an Office 365 subscription is required.