Required, unless file redirection or replacement is disabled
ObjectARX and ObjectDBX applications
If your application is using auxiliary files, you must call AcDbHostApplicationServices::mapFile() first to specify the location of your resources. If you are attempting to retrieve a file, use AcDbHostApplicationServices::findFile(). You must call the functions in this order.
If you wish to use search logic that differs from findFile(), you must still call mapFile() first. This is to give the host application and other loaded applications a chance to provide an alternate file name.
mapFile() has restrictions on the ways it can be called. For example, you may call the function if a required file has moved to a different location. But redirecting to an entirely different file may interfere with an application’s operability. For more information on the usage of these functions, please see the ObjectARX Reference Guide.
An instance where these functions are not necessary is when temporary DWG files are created by DWF underlays during DGN to DWF translation for DGN xrefs. Since these files are created and used only by that process, they are immediately deleted afterwards. Thus, no mapping is necessary.