How do I digitally sign a .pem file using the SHA256 algorithm

I have a .pem file converted from an A3 digital certificate (.pfx) I need to sign 2 CNPJs concatenated using this .pem file, which contains 2 Public and 1 Private Keys, I need to use the private key to sign the CNPJs, which in the case it will generate a base64 signature. There is a way to do this using OpenSSL, follow the link: link . But in case I wanted to know if it would be possible to do this in VB.NET language or in C #, In VB I imported (Imports System.Security.Cryptography), but could not continue. Would anyone have a hint?