Good question. Most common graphics applications generate CGM in a pretty unpredictable way. Only applications with sophisticated CGM support will allow the user to specify the profile to be used. 

So here is a small roadmap for those who want to migrate to WebCGM:

If you have CGM files without graphical objects:
This means you have version 1, 2, or 3 files, most likely version 1. Opening these files with a capable application and saving them as WebCGM files should do the job. This will not add graphical objects or hotspots though.

If you have CGM version 4 files with graphical objects:
Such files can only come from a handful of programs. Files from former InterCAP products (ActiveCGM etc) used a proprietary way to store object and hotspot information, the results of this conversion depends on the content of the files. ITEDO can certainly help you to assess the situation. Other version 4 files are most likely ATA GREXCHANGE files or files produced by IsoDraw that used a private Document Type Definition (DTD). Former ATA files can be migrated easily except for the external reference that is not supported by WebCGM. Files with private object definitions can be saved as WebCGM files, however, you will lose the private definitions.