Now you will be able to purchase a yearly Office 365 subscription when you purchase a new copy of iPad Pro. That is, when you are checking out, you will be asked if you would like to purchase a one-year subscription of the Microsoft Office 365 suite along with your iPad Pro. It will cost you $70 per year. What if you already have an Office 365 subscription? Will you be able to use it with the new iPad Pro? I guess so.
As this Engadget link says, with this move Microsoft has joined Logitech as the only non-Apple accessory-provider when you order an iPad Pro. The writer says that perhaps Apple is doing this to create more competition with Microsoft Surface, which is a tablet that uses Office 365. But I think it might also be a backdoor deal with Microsoft. If Apple sells MS Office 365 as an accessory than obviously Microsoft will also be getting its share of the revenue.
Surprisingly, you have to purchase a yearly subscription of MS Office 365 when you purchase a 12.9-inch iPad Pro. Otherwise, you can use Office 365 free, because provided the screen size of your device is less than 10.1 inch you can use the MS mobile Office products for free.