This conversion looks like attempt to transform older CAD schematics (.sch) to newer OrCAD files (.dsn), something that seems to be pretty complicated but not impossible. Your best option would be to consult Cadence support / forums, but you certainly will need OrCAD installed.
Convert CAD schematics file to OrCAD schematic capture data.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert sch 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 sch 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.