Files with dxd file extension might be found as old documents created in now discontinued program called Diogenes by Dimensione CAD.
DXD file extension - Diogenes Extended Document
What is dxd file? How to open dxd files?
File type specification:
The dxd file extension was in the past used for some sort of document format in program called Diogenes by Dimensione CAD company.
Seems like the company is out of business and the program discontinued, so this file type is most likely obsolete.
This dxd file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.