Yes, it is possible, for example by activating the application using
the AppActivate command and then executing SendKeys "%{F4}".
If the application is an automation server (Word or Excel), there is
an other opportunity using the GetObject function to get a reference
to the application and then using the applications method to quit the
application (mostly "quit"), for example:
Dim objWord As Object
Set objWord = GetObject(Class:="Word.Application")
objWord.Quit
Set objWord = Nothing