By Hugo Costa.
Make sure that gesture for App Exposé, is selected on your trackpad settings (System Preferences/TrackPad).
Put the mouse cursor over the Dock icon of the app you want to run Exposé on, and then swipe down with three fingers.
This will launch App Exposé for the app, even if it isn’t currently running!
In that case, it will show a row of recently opened documents at the bottom of the screen, which you can click on to launch the app and open the document.
enjoy!
Hugo.