"To view a PDF file, just double-click it to open it in Preview."
Mac doesn't require a third-party application to view PDFs, so why does Windows?
Heck, you don't even need to build it into the OS. Just make it an optional download such as your Save As PDF add-in for Office.
We know, we know… even though anyone is allowed to create applications that can read and write PDF files without having to pay royalties to Adobe Systems, you guys can't. You're just too big and can't ship add on PDF functionality without freaking out Adobe.
But you know what?
You really shouldn't care anymore. Freak them out.