Extracting a Public Key from a SSL Certificate

First convert the .pfx file to .pem format

openssl pkcs12 -in ClientCert1.pfx -out privpub.pem

Then extract the public key from the .pem format:

openssl x509 -inform pem -in privpub.pem -pubkey -out pub.pem -outform pem

Source

OpenSSL for Windows