purchasing microsoft office for ipad from apple

You can do it by downloading one of the apps (e.g., Word) and then subscribing via an in-app purchase. You download the app through the App Store app -- search for Microsoft and then download each app separately (Word, Excel, etc).

I would however strongly recommend that you purchase the Office 365 license directly from Microsoft instead and avoid potential issues of having an additional party involved. https://www.microsoft.com/en-us/p/office-365-home/cfq7ttc0k5dm?activetab=pivot%3aoverviewtab

You would still download the apps as described above.