Selecting all the clips on your timeline should be simple but unlike many pieces of software, using the standard Command+A (Control+A on PC) in Pro Tools doesn’t select all the clips on every track, it selects all the clips on the track your selection point is currently on.

Select All Clips

To select all clips you should first hit Return and take your insertion point back to the beginning of the session, then hitting Command+A (Control+A on PC) will select all the clips on every track.