Find a software converter able to convert prj files to pdf files.
A lot of programs have used .prj files for the projects in the past and perhaps still some are. Often a PDF function is available to either export the output of the project as PDF documents or provide some sort of reporting function that creates .pdf files.
You can also use the default Print function to produce PDF documents, if you have a virtual PDF printer installed on your computer.
Unfortunately, there is no detailed software record in the database for this conversion.
Articles and other information relating to prj 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
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