What iOS version is required for Microsoft Office 365 on iPad Pro?

If considering a refurbished iPad, ensure that it supports iPadOS 17 or later - this being the current minimum version of iPadOS for Microsoft's iPadOS compatible Apps. That said, to ensure that you don't need to replace the iPad again any time soon, you would be well advised to only consider an iPad that supports iPadOS 18.

For information, here is a list of the highest version of iPadOS supported by the "recent" older and current models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

iPad5, iPad Pro (9.7"/12.9" 1st generation)* - iPadOS 16.7.10

iPad6, iPad Pro (10.5"/12.9" 2nd generation) - iPadOS 17.7.5

(*) obsolete

Newer models are all able to be updated to the current version - iPadOS 18.3.1

• iPad Pro 13" (M4)
• iPad Pro 12.9" (3rd generation and later)
• iPad Pro 11" (1st generation and later + M4)
• iPad Air (3rd generation and later + M2)
• iPad (7th generation and later)
• iPad mini (5th generation and later + A17 Pro)

Be aware that you cannot install Office 365 Windows PC software on your iPad. However, there is now an Office365 App in the Apple App Store for both iPad and iPhone.

• Microsoft Office

https://apps.apple.com/gb/app/microsoft-office/id541164041

The Office 365 App for iPad is a “cut-down” single install App; this App does not replicate full MS Office functionality. But this is not the end of the story. 

There are individual Microsoft Apps for Word, Excel, PowerPoint, Outlook etc. intended for iPad. iPad models with a screen size of less than 10.1” can access a restricted set of App features, including creation and editing of documents, for free. 

For iPad devices with a screen larger than 10.1”, the MS App’s require an active Microsoft 365 Subscription - which you are already likely to have. If you don’t have an active O365 subscription, functionality is limited to opening and reviewing existing documents.

All the Microsoft Apps for iPad can be found in the Apple App Store.

Microsoft Word, Excel, PowerPoint, Outlook and others are all available from the Apple App Store. All require iOS/iPadOS13 or later.

• Word

https://apps.apple.com/gb/app/microsoft-word/id586447913

• Excel

https://apps.apple.com/gb/app/microsoft-excel/id586683407

• PowerPoint

https://apps.apple.com/gb/app/microsoft-powerpoint/id586449534

• Outlook

https://apps.apple.com/gb/app/microsoft-outlook/id951937596

• Teams

https://apps.apple.com/gb/app/microsoft-teams/id1113153706

• OneDrive

https://apps.apple.com/gb/app/microsoft-onedrive/id477537958

• Authenticator

https://apps.apple.com/gb/app/microsoft-authenticator/id983156458

• OneNote

https://apps.apple.com/gb/app/microsoft-onenote/id410395246

In summary, MS Productivity Apps for iPad (such as Word, Excel, PowerPoint) offer limited functionality without an Office 365 Subscription - but only for devices with a screen size of 10.1” or less. Devices with larger screens only permit you to view (but not create or edit) an existing document. Full App functionality requires an active Office 365 Subscription.