During these years it happened that often some end users had problems to read on their computer .p7m files.
For that purpose and considering that finding suitable free tool for me was not immediately straight I take note of software that worked fine for me.
DigitalSign Reader 5.0
http://www.comped.it/it/prodotti/digitalsign-reader/digitalsign-reader-5-scaricalo-subito
I hope that this information could be useful for someone.