Recommendation
ObjectARX and ObjectDBX modules
When a host application encounters an instance of a custom object class that does not have an application loaded, it will create "proxy" objects and entities, which have limited capabilities. To avoid this, register your Object Enabler to be demand-loaded when an instance of your custom object is encountered in a DWG or DXF file. You should generally expose database and view-specific behavior in Object Enablers.
For a particular release, DWG and DXF file formats must be compatible with each other because they represent the same data in different ways.