Convert crt and key to pfx using pure c #

Without using any third party libraries, how can you convert .crt and .key to .pfx using only C # code?

I already know how to do this on the command line with openssl. I am looking for a solution that only uses what is available in the .NET Framework 4.0-4.5.2.

To clarify that there are no third party libraries, the following are examples of third party libraries:

• BouncyCastle - library
• openssl - using command line or embedding
• makecert - command line usage