Despite the existence of OneDrive, Microsoft and Dropbox are friends now. The Redmond-based company knows where you're saving your stuff, and it wants you using its office suite regardless. It's business.
So Microsoft and Dropbox have announced the next level of integration for their mutual products. Office Online will now let you open a file straight from Dropbox, edit it, and save it back. This is the kind of seamless experience that came to Android towards the end of last year.
This is all part of Microsoft's continued strategy to integrate Office with whatever platforms and cloud storage providers it can get its hands on. With competitors hoping to eat away at the company's dominance, it can't afford to let stubbornness get in the way of a new customer. Office has to pay the bills.