CAMtastic 2000 Viewer is an old application developed by Innovative CAD Software which seems to be discontinued and no longer supported. Unfortunately, there is no information about its converting capabilities and in order to convert the .dxf file in a Gerber one, I suggest you use ViewMate Pro. The software is shareware and it can be tested free of charge if you download and install its trial version. Press the blue Try Now button, fill up the provided form and press Start your trial. If you're not satisfied with ViewMate Pro functions, you can use GerbView. It is also a shareware product that can be tested free of charge.