If you want to split and .pfx file to see the Prvate key, you need to use OpenSSL to do this.
Download the installer from here: https://slproweb.com/products/Win32OpenSSL.html
Place your certificate in C:
You’ll need to know the password for your PFX file.
Open a CMD and change directory to C:Program Files OpenSSL-win64bin
Then run these three commands:
openssl.exe pkcs12 -in c:certname.pfx -nocerts -out key.pem -nodes
openssl.exe pkcs12 -in c:certname.pfx -nokeys -out cert.pem
openssl.exe rsa -in key.pem -out server.key
The private key is output into the key.pem file. Open this in notepad. They will be located at C:Program Files OpenSSL-win64bin