Hi Pawan,
The .pfx can be installed by using ASDM.
In order to install it using the CLI you first need to convert the file to be base64, you can do it with OpenSSL and using the following command:
openssl base64 -in certificate.pfx -out certificate.p12
Then, you use the following commands on the CLI of the ASA:
ASA(config)# crypto ca trustpoint SSL-Trustpoint-PKCS12
ASA(config-ca-trustpoint)# enrollment terminal
ASA(config-ca-trustpoint)# exit
ASA(config)# crypto ca import SSL-Trustpoint-PKCS12
<base64 format file>
Quit
Rate if it helps.
Regards,
Josue Brenes
TAC - VPN Engineer.