ocd to kml conversion most likely covers the export of the default digitized map format (.ocd file) from OCAD cartography software to Google Earth vector format (.kml files).
According to OCAD's wiki, such export is possible, but works only for either selected map objects, or point, line and area objects and does not work for text objects.
We are not aware of any 3rd party software that can be otherwise used to convert ocd to kml, simply because .ocd file appears to be exclusively supported in OCAD.
Updated: January 2, 2024