DER to PEM converter

The DER to PEM converter turns binary DER files into PEM text. Choose a .der, .cer or .crt file and press Convert; the tool recognises what the file contains and shows it as PEM, ready to copy or download. Conversion happens in your browser.

When you need DER to PEM

• You downloaded an intermediate certificate from the CA Issuers URL in a certificate. CAs serve these as DER (application/pkix-cert).
• Windows exported a certificate as "DER encoded binary X.509 (.CER)".
• A Java or hardware appliance produced a DER key or CSR.

Steps

1. Choose the DER file.
2. Press Convert.
3. Copy the PEM text or download it. Append intermediates to your fullchain.pem after the leaf certificate.

Equivalent OpenSSL commands

openssl x509 -inform DER -in cert.der -out cert.pem          # certificate
openssl req  -inform DER -in request.der -out request.csr     # CSR
openssl pkey -inform DER -in key.der -out key.pem             # private key

Common errors

• "Could not recognise this binary file": it may be a PFX (use PFX to PEM) or not a certificate at all.
• The PEM output has the wrong header: software is strict about BEGIN CERTIFICATE vs BEGIN TRUSTED CERTIFICATE; this tool writes standard headers.