BC's Autodesk Forge integration processes files based on MIME-type rather than their file extension.
By default, files with the following MIME-types set will be sent for processing.
- 'application/x-navisworks'
- 'application/x-revit'
In most cases, this should translate to Navisworks (.nwd) and Revit (.rvt) files, but will not necessarily in every case.