The only opj to pdf conversion that would make sense, is export of OrCAD designs as PDF documents. It seems the program has no default PDF export function and you need to install one of the many PDF export plugins or virtual PDF printers in order to export your designs as .pdf files.
Convert OrCAD capture project to Adobe Portable document format.
We found one software available in the database for this conversion.
Articles and other information relating to opj into pdf conversion:
How to print anything to PDF using virtual PDF printer - Create PDF documents from any Windows application that is capable to print using PDFCreator
Microsoft Windows software - convert opj to pdf on Windows
A modeling suite used to design printed circuit boards
Convert from opj file format
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.