What are file name extensions used for certificates? I see .cer files on my Windows computer.

Most commonly used file name extensions for X.509 certificates are:

• .cer - Used for certificate files in binary DER format. Could also be used for certificate files in text PEM format.
• .crt - Used for certificate files in binary DER format. Could also be used for certificate files in text PEM format.
• .der - Used for certificate files in binary DER (Distinguished Encoding Rules) format.
• .pem - Used for certificate files in text PEM (Privacy Enhanced Mail) format. PEM format is the Base64 encoded version of the DER format enclosed between "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----".
• .p7b or .p7c - Used for certificate files in PKCS#7 (Public-Key Cryptography Standards #7) format. Could also be used for certificates in the Base64 encoded version of PKCS#7 format enclosed between "-----BEGIN PKCS7-----" and "-----END PKCS7-----".
• .p12 - Used for certificate files with certificates and private keys together in PKCS#12 (Public-Key Cryptography Standards #12) format.
• .pfx - Used for certificate files with certificates and private keys together in PFX (Personal Information Exchange) format, which is the predecessor of PKCS#12.