You can convert a PAR-File to a sheet metal File but not it's Format / not directely to a *.psm. The file extension remains *.par. But if you need the PSM-Extension you could "change" its Format to *.psm and it's working!
I guess it really depends on what your part model looks like, and if the desing can actually be processed as a sheet metal model.....but here's a video that shows the process.
Design Manager Streetscape Limited
Solid Edge ST10 [MP0] Classic [x2 seats]