We loved to hate Microsoft Windows because it was such a vulnerable system. Now Gates & Co., however belatedly, are integrating safeguards and the independent purveyors of Band-Aids are upset. This, I say, not a big deal, only what Microsoft ought to have been doing all along.
The idea of a PDF compatible browser and editor isn't new; there is open source software on Linux for that. Microsoft will find it difficult to embrace/extend/extinguish Adobe anytime soon because PDF has a goodly established base in UNIX/Mac world.
They mainly won't be able to do it because PDF has mindshare and many consider it synonymous with portable documents, just like Windows does with operating systems. The PDF format is open, but no program can say it's writing a PDF unless it conforms to PDF standards. To do otherwise is violating Adobe's license and trademarks. And a Microsoft document export wouldn't be popular, because it isn't "PDF."
IOW, Microsoft would have a hell of a court case if it tried embrace-extend-eliminate with PDF. It would also have a problem reaching the printing market, which lives and breathes on exact-to-standard PDF files.