.DEP4 File

The dep4 file extension is used for one of the Data Exchange Protocol files. The data exchange protocols (DEP) define logical sets of the complete data at defined stages in the process, from analysis through design and fabrication.

The dep4 file contains detailing data. 

Seems like it was used in the past in some 3D engineering software.

This dep4 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.

How to open:

Probably not meant to be accessed by the user.

How to convert:

Probably cannot be converted to anything else.