It seems that C3 to DKB is very specific and rather uncommon graphics conversion. However as far as we known POV-Ray with Moray Plugin should be able to export *.c3 files (Pov-Ray) as *.dkb files (DKBTrace graphics).
Convert Pov-Ray for Windows 3.1 scenes advanced newltpot file to DKBTrace raytraced graphics file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert c3 to dkb on Windows
A free 3D graphics tool
Convert from c3 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.