As a product line that has already made a successful move from the PC desktop to the cloud and various popular mobile devices, it's perhaps not surprising that Office played a big role in the opening day keynote of Microsoft's Worldwide Partner Conference. But Office is even more central to Microsoft's future than is perhaps immediately obvious. And with the firm's new focus on productivity, Office is in fact the linchpin of Microsoft's go-forward strategy.

If you haven't yet, you can check out my overview of the opening WPC keynote in WPC 2014: Microsoft Has a "Challenger Mentality" in Mobile First, Cloud First World. Here, I'll focus just on the Office bits, which of course includes Office 365.

Office is huge. There are over 1 billion active users of Office, making it one of the most popular software platforms on earth.

Office 365 is huge. While Microsoft didn't supply new Office 365 user base statistics, it noted that it is the fastest-growing business in Microsoft's history. Last year, Office 365 was a $1 billion business for Microsoft, a key milestone. But this year it's $2.5 billion at mid-year and still growing rapidly. And 60 percent of the Fortune 500 have purchased Office 365 in the past 12 months alone. Since it debuted in fiscal year 2009, Office 365 has experienced triple digit growth every year.

With a productivity focus, Office is key. In his open letter to employees last week, Microsoft CEO Satya Nadella said, "At our core, Microsoft is the productivity and platform company for the mobile-first and cloud-first world. We will reinvent productivity to empower every person and every organization on the planet to do more and achieve more." At Microsoft, Office is the key to, and the core component of, its productivity efforts. He may as well have just said that Microsoft was an Office company and that it would push Office hard in both mobile devices and the cloud.

Office is cross-platform. You can run Office Online on a Chromebook. You can run Office Mobile on Windows Phone, iPhone and Android. And you can run Office on the iPad, with Android and Windows Touch versions coming soon (see below). "Office is cross platform," Microsoft COO Kevin Turner said. "We are going to win in productivity. Period."

But it's better on Windows. Office will work on competing platforms, but "the best Office mobile experience is on Windows and Windows Phone 8.1," Turner said.

Office for iPad. Microsoft noted that iPad users had downloaded 27 million copies of Office for iPad, though that figure isn't new. (The company first supplied it in May, as it turns out.) And of course, that number is divided somehow between three apps (Word, Excel, and PowerPoint). And we don't know how many have led to Office 365 subscriptions. (My suspicion is that most users already had an Office 365 subscription before they got the apps.)

Office Touch is coming to Android, Windows. Since Microsoft launched Office for iPad in late March, there's been some grumbling from Windows users who are hoping to see Office Touch for Windows appear sooner rather than later. My sources suggest that Office for Android tablets—which should be very similar if not identical to the iPad version—will appear first, sometime this year. And that Office Touch for Windows could be delayed until next April, when it will ship alongside Windows 9 "Threshold." Microsoft didn't really provide much more information about this product, but it reiterated that it was still happening.

Microsoft partners will soon be able to sell and provision Office 365 (and Intune) and do so with a single bill. This is a big deal, since partners could previously get their customers started on Office 365, but then basically handed off the relationship to Microsoft.

Office 365 apps. Over 5 million apps for Office 365 and Azure have been installed by customers.

Office 365 Pro Plus. Given the confusion between the recently-announced Office 365 Business offering and Office 365 Pro Plus—see Microsoft Announces Major Changes to Office 365 for Small and Midsized Businesses, but the short version is that they're subtly different—I found this bit to very interesting. "This is the future of where we take Office," Mr. Turner said. Huh. I think he was speaking generally, and that what he meant was that Office as a service—including the actual PC-installable Office software—was the future of where Microsoft takes Office. That is, it represents a licensing change.

OneNote. Microsoft explicitly called out OneNote, noting (ahem) that this incredibly useful and cross-platform solution was being underserved by the company that makes it. "We've done poor job marketing OneNote," Turner said.