Decrypting with signed pfx file

Is it possible in c# .net to decrypt an encrypted string using the same
pfx file who's public key was used to encrypt that string?

I have an old asp page that uses persit's aspencrypt object and a pfx file to encrypt and decrypt  a string.

I have the private key in that same pfx file but I don't have a clue as
to how  to decrypt that string using pure c# .net but I can do
this in c# using aspencrypt like so:

using ASPENCRYPTLib;

public string decrypt(string passedIn)
{
       //  Aspencrypt variables.
       string decrypted = "Failed to decrypt.";
       ICryptoManager manager = null;
       ICryptoStore store = null;
       ICryptoCert certificate = null;
       ICryptoContext context = null;
       ICryptoMessa ...