A DER file is a digital certificate file that is created and stored in binary format. It is a binary encoding for the X.509 certificates and private keys. In contrast to PEM files (CRT, CER), DER files do not contain human-readable plain text statements such as —–BEGIN CERTIFICATE—–. They are mostly used in context of Java.
DER File Format - More Information
DER Files are stored to disc in binary file format that is not human-readable. These certificate files are loaded and recognized by standard web browsers for secure navigation.
How does a DER-encoded certificate look like?
An example of a DER-encoded SSL/TLS certificate is as shown below.