siemens pc adapter 6es7 972-0ca23-0xa0 PC adapter driver comes with Simatic Net. It does not have separite CD with it like the PC adapter USB.
To install its driver, just setup Simatic Manager and then Open control panel, Set PG/PC interface, and select PC Adapter (MPI). You should have two options (COM) & USB. Select COM and then adjust baud rate. Baud rate should match the dip switch in the PC adapter side. It can be 19200 or 38400.
You can not use for this adapter PC adapter (Auto) option as this option is applicable for PC adapter with USB interface.