We do not know about any possible conversion for .camthtr and .camproj files, except that they both originate from Camtasia Studio. If you are particularly interested in conversion of Camtasia files, perhaps contacting the support of the software's developer would be the wisest thing to do.
Convert Camtasia Studio theater file to Camtasia Studio project.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert camthtr to camproj on Windows
A screen capture and video editing software
Convert from camthtr 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.