To extract the OpenVPN driver code signing certificate, download OpenVPN from here: https://openvpn.net/index.php/download/community-downloads.html (this article was created using version 2.3.10)
On a test machine, install as administrator.
Click I Agree
Ensure that only TAP Virtual Ethernet Adapter is selected and click Next
On the windows security dialog, tick Always trust software from “OpenVPN Technologies, Inc.”.
and click Install.
Once installed, click Next
Open the MMC
Click File and select Add/Remove Snap-in…
Select Certificates and click Add.
Select Computer Account and click Next
Select Local comptuer: (the computer this console is running on) and click Finish
Expand Certificates (Local Computer) –> Trusted Publishers –> Certificates.
Right click the OpenVPN Technologies certificate and select All Tasks –> Export…
Select Base64 encoded x.509 (.CER) and click Next
Click Browse, navigate to the location you wish to save the certificate and click Next
The certificate is now in the location specified.