Starting with Windows 8, Microsoft will be including native PDF support in its Modern Reader application.
As reported, Modern Reader provides a very simplistic interface to quickly view PDF files. It's also one of the first apps to utilize the AppX application model. AppX has been designed for Windows 8 and is very reminiscent of the application packages used in Windows Phone 7. Within Windows believes that Microsoft may provide a unified application type for Windows 8 and Windows Phone 8 providing developers the ability to easily develop and deploy apps for both platforms.
Windows 8 looks to continue the trend of Windows 7 of providing built-in support for a variety of features and functionality that used to require third-party apps. In Windows 7, we saw added support for popular third-party video codecs as well as native support for burning ISO image files. With native support for PDF files in Windows 8, this brings Microsoft's OS on par with its competitors as well as providing the much required OS-level support for many applications that currently use the PDF format.
Here're a couple of screenshots: