PEM is the most common format for X.509 certificates, CSRs, and cryptographic keys.
A PEM file is a text file containing one or more items in Base64 ASCII encoding, each with plain-text headers and footers (e.g. -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----).
A single PEM file could contain an end-entity certificate, a private key, or multiple certificates forming a complete chain of trust. Most certificate files will be in PEM format.
PEM file name extensions
PEM files can usually have the .crt, .pem, .cer, and .key extensions (for private keys), but you can also see them with different extensions. For example, the CA bundle file has the .ca-bundle extension.
Convert SSL Certificates
There are different reasons why you might want to convert your certificates to other formats. For more information on how to convert SSL certificates, read more about it in the following article