Microsoft is forgoing as much as $2.5 billion a year in extra revenue by not yet putting a full-fledged version of its Office suite on Apple’s iPad. That’s the estimate by Morgan Stanley analyst Adam Holt, as reported by Fortune magazine today.

There were a series of reports last year that Microsoft was working on a version of Office for the Apple tablet, but the company has clearly been wrestling with this one. Putting a real version of Office on the iPad might be good for Office, but it also would be a tough pill to swallow for the Windows business, taking away or diminishing one of the key points of differentiation for the new wave of Windows tablets.

Microsoft’s chief financial officer, Peter Klein, was asked about this at the Goldman Sachs technology conference yesterday. Here was the exchange:

HEATHER BELLINI: … A lot of questions about Office on iOS. What do you have to do to get it there? What are the reasons why you wouldn’t bring it there ultimately as you think about how that would maximize profit for that division?

PETER KLEIN: I’m sure you can imagine the tradeoffs. We think about it a lot. We have a history of cross-platform delivery broadly in productivity, whether it’s Office on the Mac, or whether it’s certain experiences that apply that customers really want across platform, whether that’s e-mail, communications, note-taking. So, we deliver all those products cross-platform, Exchange, Active Sync, SharePoint, OneNote, and a whole bunch of things. And, importantly with the web applications you can do — you can access Office documents, do some light editing on any device, and on any browser.

And so there’s a lot of things that we’re doing to meet that need, and then we’ll continue to think about other things going forward.

That reference to Microsoft thinking about “other things” clearly leaves the door open to seeing some form of Word, Excel and PowerPoint et al in an iOS app from the Redmond company. But my bet is that Microsoft will offer something much, much less than a full-featured version of Office if it does decide to walk through that door.

By the way, according to Fortune, the Morgan Stanley estimate for Microsoft’s potential annual revenue from Office on the iPad is based on an estimated installed base of 200 million iPads in 2014 — and the number would be after Apple takes its 30 percent cut.

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