Not sure you can do this. According to
this thread, the only way to make a desktop app communicate with a metro app (on the same PC) is to use a WCF web service! :o
You can also have a look at this
thread. You can use ShellExecute to open a document. If the document type is associated to a Metro app, then ShellExecute will open a Metro app.
Otherwise, if you are writing a desktop debugger which must run Metro apps, then you can use
IApplicationActivationManager interface.