Metro is a new document file format, similar in many ways to PDF. It's also a spool format. When you print on a Windows or a Mac computer, the print system has a format that it uses to communicate the data through the print subsystem and spool it to the device. And it's also a page description language, similar to PCL PostScript, that can be used to transmit that information all the way down to a printer, where it turns into the data that comes out on a piece of paper. And Metro is very tightly related to this thing called WinFX.
In an interview to PDFzone, Adrian Ford, explains how Metro differs from PDF and what are the similarities in the two formats.
How is Metro similar to PDF?
Like PDF, you can have a Metro document that sits on disk and that you share with other people and e-mail around, and that document contains all the graphical data and resources and images and fonts and everything else, and supports compression in an efficient container, and people can view that document in a viewer that isn't related to content creation applications. In that sense the format does have similar characteristics with PDF.
Also, if you look at the specifications for PDF and for Metro they have similar functionalities defined within them.
How does Metro differ from PDF?
One of the key things about Metro is the use of it within the print subsystem on Windows. There are number of issues and limitations you have to face printing on Windows. The application developers or printer-driver developers have to work extremely hard to make those things work and to bypass these limitations in the print subsystem.
Today you could have an application that understands RGB wide-gamut photo printing, but the application can't send that data through the print subsystem to a printer because that extra information gets lost. So today you often get software that bypasses the print subsystem, and you can't go file to print nice pictures on your Epson printer. There are a number of real issues that Metro solves on the print side that PDF doesn't solve.