It seems this specific OPJ to DSN conversion is only possible within OrCAD PCB Designer. These special *.opj projects are only created with OrCAD and only this software can open and work with them.
Convert OrCAD capture project to OrCAD schematic capture data.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert opj to dsn on Windows
Orcad PCB Designer is printed circuit board design suite, that includes a constraint manager, design capture technology, component tools, a PCB editor, an auto/interactive router, and interfaces for manufacturing and mechanical CAD.
Convert from opj file
to dsn file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.