Camtasia supports export to the AVI format by default, so you can use the existing share and publish function to export projects as .avi videos. A .cam file probably originates from some very old version of Camtasia, so the latest versions of the program may not support it. You would have to use some older version.
Convert Camtasia Studio project file to Audio Video Interleave movie.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert cam to avi on Windows
A screen capture and video editing software
Convert from cam file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.