The .cer file format is one of the most common file formats for storing certificates in. It is usually PEM encoded but may also be DER encoded. If it is PEM encoded it can contain one or more certificates, if it is DER encoded it will contain only a single certificate.
You can recognize PEM encoded files by the readable
BEGIN CERTIFICATE and
END CERTIFICATE markers in the file. Our online conversion supports converting certificates from and to the .CER format.