Open Office files from Finder in the same screen
Apple's website:


  If you work in multiple spaces, you can assign apps to particular spaces.
  
  Press and hold an app’s icon in the Dock. You may have to first open the app from Launchpad to see its icon in the Dock.
  From the shortcut menu that appears over the icon, choose one of these:
  To have the app open only in the current space, choose Options > This Desktop. From now on, the app will open in the current space; if you are working in a different space, the app’s space scrolls into view.
  
  This setting doesn’t apply to full-screen windows, which always appear in their own separate spaces.
  
  To have the app open in every space, choose Options > All Desktops. From now on, when the app is open it will appear in every space.
  
  To have the app open in the space you are currently using, choose Options > None.
  
  In Mission Control preferences, you can specify that when you switch to an app, your desktop should scroll to a space with open windows for that app.


THis should allow you to choose Office programs to open in that desktop