Following are the steps to Export an SSL Certificate from the Windows Server:
On the Start menu, click Administrative Tools, and then click Internet Service Manager.
Select the server name of IIS then Click on Server Certificates option.
You will have a list of the SSL certificates hosted on the Server. Select the certificate which you want to export, right click on it and select Export Option. OR you can directly click on Export link from the Actions panel.
Now, you will see Export Certificate dialog box, in the Export to text box, write name of file with full path where you want to save your .pfx file or you can also click on the (…) button and navigate to the path and assign filename for exporting.