Open Pro Tools. Once open, click "Track" and select "New Track."
Select "Stereo" and "Audio" as the new track parameters and click the "Create" button.
Double-click the name of this track and change it to "Stereo Bounce."
Open the "Mix" window and click the "input" button on this new stereo audio track.
Set the input of this stereo track to a stereo bus, such as "Bus 1-2."
Click the "output" button on all of the mono files you want to bounce to stereo.
Select "Bus 1-2" as the output for these mono files.
Click the "Record" button on the stereo track you created to arm it for recording.
Open the "Edit" window.
Click the "Record" button at the top of the "Edit" window to arm Pro Tools for recording.
Click "Play" to bounce the mono files to stereo.
Click the "Stop" button when the mono files finish bouncing.