If you wish to install exported SSL with .pfx file to your cPanel server. You may refer to the following step.
Assume, you have a file named domain.pfx.
1) Export key file,
#openssl pkcs12 -in domain.pfx -nocerts -out domain.key
2) Export decrypted key file,
#openssl rsa -in domain.key -out domain.decrypted.key
3) Export Certificate, crt file,
#openssl pkcs12 -in domain.pfx -clcerts -nokeys -out domain.crt
4) Export cabundle file,
#openssl pkcs12 -in domain.pfx -cacerts -nokeys -out cabundle.pem
5) You should now able install your SSL through WHM.