Microsoft has released free iPad versions of Word, Excel, and PowerPoint. All are optimized to fit iPad screens, and require a qualifying Office 365 subscription to be able to create or edit documents (you can view documents for free).
Qualifying Office 365 subscriptions include: Home, Small Business Premium, Midsize Business, Enterprise E3 and E4 (Enterprise and Government), Education A3 and A4, ProPlus, and University.
If you buy an Office 365 subscription as an in-app purchase through the iPad versions of Word, Excel, or PowerPoint… it will automatically renew within 24 hours prior to the end of the subscription period. To avoid this you must disabled auto-renewal beforehand by going to your iTunes account settings. A subscription cannot be cancelled during the active subscription period.