Teaming stores the default "file extension to program mapping" information in the ssf.properties file located in <tomcat>/webapps/ssf/WEB-INF/classes/config directory. To find the relevant section in the configuration file, search for the text "Edit in Place".

For instance, to register the file extension dxf with Teaming, you would want to add it to the value of the edit.in.place.file.applet.extensions property. Then, assuming you're running the authoring program on Linux, you would add a new properly that looks like the following:

edit.in.place.linux.editor.dxf=<your client-side authoring program for the file extension>

Then, re-start Teaming server to bring the changes to effect.

It is important to note that, in order to take advantage of the Edit feature with above setup, the authoring program MUST be able to handle WebDAV protocol for accessing source files remotely. Otherwise, this setup will not do any good. I'm not familiar with the dxf files, so I can't tell whether it supports WebDAV protocol or not.

One more note - you'll probably want to copy that property (and make your changes to it ) into the ssf-ext.properties file.  That way they won't be overwritten when you upgrade teaming.