Extraction of the certificate of a digitally signed files (p7m)

Let's consider the case where the signed document is a pdf (document.pdf.p7m).

To extract the certificate used to sign the p7m we use the openssl command with the pkcs parameter

openssl pkcs7 -inform DER -in document.pdf.p7m -print_certs -out cert.pem

The certificate will be extracted in the cert.pem file. If you want to display textually enough the certificate command x509

openssl x509 -in cert.pem -text -noout

For more information, see the articol