You cannot do a direct conversion of a layout from Pr0tel to C@dence.
The best you could do would be to export the netlist from Pr0tel, then use that netlist in Allegr0 or 0rcad. There are several different netlisters available on the @ltium website. See: https://www.altium.com/Community/Support/Downloads/ and look under "Additional Output Generators".
You could also output a .DSN file that can be used by C@dence layout software.