PEM, CER, CRT, KEY(PrivateKey) , PFX

https://www.namecheap.com/support/knowledgebase/article.aspx/9617/69/how-to-convert-certificates-into-different-formats-using-openssl

https://www.ssl.com/guide/pem-der-crt-and-cer-x-509-encodings-and-conversions

https://www.sslshopper.com/certificate-decoder.html

openssl x509 -in certificate.crt -text -noout