Use openssl to extract private key. After executing the following line. you will need to enter the password used when the pfx file was created.
openssl pkcs12 -in file_name.pfx -out certificate.cer -nodes
When converting a PFX file to PEM format, OpenSSL will put all the certificates and the private key into a single file. You will need to open the file in a text editor and copy each certificate and private key (including the BEGIN/END statments) to its own individual text file and save them as certificate.cer, CACert.cer, and privateKey.key respectively.