If you have an SSL certificate, then chances are that it is in one of the following formats.
The most common format is a DER-encoded public key certificate. This type of certificate contains a public key and a corresponding private key. The private key is kept secret, while the public key is used to encrypt data. The DER format specifies the type of encoding used for the certificate, along with other information such as the length of the certificate, validity period and so on.
An X509-encoded certificate can be considered a more advanced form of DER-encoded certificate. It can be used to authenticate both clients and servers securely, and it also allows for some extra features such as digital signature verification, including digital signatures from third parties.
Another type of SSL certificate is PEM-encoded certificate. This type of certificate contains an encrypted version of your private key and is used by your web server to encrypt data before sending it across the network.