Back up your SSL certificate: Plesk
We recommend that you back up your SSL certificate and its corresponding private key so that you’re safeguarding against any disasters disrupting your server. These instructions will also help you export your certificate from one web server and import the certificate and its private key to another web server.
Plesk stores the SSL related files in a httpd.pem file inside a “cert” folder. Both the RSA Private Key and Certificate are kept inside this file the path to which is:
Back up the RSA private key from this folder.