Generally speaking, most .prt files (3D part / CAD) can be converted to common 3D object .obj files with most of the programs that produce their respective .prt files. Many programs use PRT format to store their 3D data, so it is many different file types just sharing the same extension.
Sometimes a good 3D conversion solution may also be of use. You can find programs, or even online conversion services, that support many variants of prt to obj conversion.