Projects (.prj) with technical drawings or some other CAD data can be usually opened and exported to one of the common CAD formats, including the exchange DXF format. Such prj to dxf conversion can be done in any program that supports this type of .prj files. A prj to dxf conversion might not be possible for every .prj file, as there are many file types using prj file extension.
Open PRJ file Open DXF file