If you have a .pfx file and you need it’s private.key, then you can use OpenSSL for extracting .pem from .pfx ( the openssl software is available at openssl.org )
To export the private key ( .pem ) from the PFX file and save it to a PEM file :
$openssl pkcs12 -in /path/to/file_name.pfx -nocerts -out private_key_name.pem
If you want to remove the password from the private key file :
$openssl rsa -in private_key_name.pem -out new_private.pem