Stop video (something like a screenshot) in Hitfilm 3 Express
The usual way to do this is with a speed effect.  Create a cut around the one frame you want to render as a still.  Your timeline should look like this:

motion-before | single frame | motion-after


You can then place a speed effect on the single frame, slow it down to 0% playback speed, and it will happily play forever if you want.  Stretch single frame to 5 seconds of length (120 frames at 24fps) and then composite your text on top.

People do this all the time.  Some applications have a "freeze frame effect" which is precisely setting the speed to zero for a default number of seconds.