Files with the .PEM extension contain certificates encoded in accordance to the Base64 standard, which is used for verifying trusted websites, for example in the X.509 standard, using a certificate base. PEM certification files are generated automatically, and they should not be opened or edited manually.

The PEM format is usually used by Unix servers based on the Apache Web software; it is compatible with OpenSSL applications. Some webpages can request that their users upload PEM files for the purposes of identity verification.