After you pay a fee, your certificate is transmitted to you as an email or file attachment. Then, you copy the contents from the CA certificate into a text file to create your own certificate file.
Open the certificate email or file.
Select the file contents between the header and trailer text.
Make sure you exclude the header and trailer.
Copy the contents of the certificate to the buffer.
Create a new text file.
Paste the certificate file contents into the empty file.
Save the file as machine name.cert.
Where:
machine name is the name of the computer that is hosting the SME/KS files.
The .cert extension is arbitrary. Certificate and key files can have any extension, but the extension you use should imply the contents of the file.