Add custom ssl certs, now available for everyone. How to?

So in the recent update 0.9.14.6 (23.des) we can now add our own custom ssl certs.
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I'm not familiar with pkcs#12.
I however have been using Letsencrypt to get my free signed ssl certs for all my standalone and apache web servers. How can I use does certs in Plex?

Edit: Available cert files from Letsencrypt: cert.pem chain.pem fullchain.pem privkey.pem