title: Get a list of opened windows cocoa
body: <p>I'm new to Cocoa and I want to know how I can get a list of all open windows. I'm not talking about running programs, since this would be an easy task. I want to list windows, for example, if I have Preview running with 10 pdf opened, my program should be able to retrieve a list with all those pdf. 
  I also want to know if there's some API available to interact with already open windows (and maybe move them or do something else) from an external application.
  Thank you.</p>