Camtasia supports export to the MPEG-4 (.mp4) format by default, so you can use the existing share and publish function to export projects as MP4 movie. A .cam file probably originates from some very old version of Camtasia, so the latest versions of the program may not support it and you might have to use some older version to achieve direct cam to mp4 conversion.
Updated: June 20, 2022