Open the Pro Tools application.
Select "File," and then choose "Open Session." Select the audio project you want to use.
Press and hold the right arrow key on your computer's keyboard to fast forward through the song in Pro Tools. Continue holding the key until you have reached the point you want to end the song. Release the arrow key as soon as you hit this point. The red playhead will be stopped at this point in the song.
Scroll to the right in the program and continue scrolling until you have reached the point in the song where all audio tracks have ended. Look for a single audio marker within the music measures section on Pro Tools. The marker will appear as an arrow pointing to the left. Click and drag this arrow to the left. Move this arrow marker to be directly in line with the red playhead. The song now ends exactly at this point. You can slide the marker back to right to lengthen the song.