Microsoft is planning on including its own Portable Document Format (PDF) reader in Windows 8 called Modern Reader. This is the first app discovered to be utilizing the new AppX application package type, as revealed by Rafael Rivera and Paul Thurrott and posted at SuperSite.
Modern Reader displays PDFs just as you would expect. It includes functions for zooming in and out, and it also has a page scrubber on the side of the application window for document navigation (a Back button appears in the upper left corner so you can return to your previous spot). It also supports side-by-side page views.
Windows does not include its own PDF reader. This is likely because of how popular the operating system is: Adobe has made it clear in the past that Microsoft would never get away with such a move.
Back when Microsoft was developing Office 2007, it promised to support exporting to PDF. Adobe made legal objections, and Office 2007 originally did not offer PDF support out of the box, but rather as a separate free download. As of Service Pack 2, however, Office has allowed users to natively save their document as PDF files.
We're not sure if Microsoft has talked to Adobe about the new feature for Windows yet. It might be alright if it's only a PDF reader, but then again, Microsoft has had many similarly simple antitrust issues to deal with before.