A tester demain pour voir si mon PC est vulnérable.

With openssl:
openssl x509 -enddate -noout -in file.pem

The output is on the form:
notAfter=Nov 3 22:23:50 2014 GMT

openssl pkcs12 -in client_ssl.pfx -out client_ssl.pem -clcerts

openssl pkcs12 -in client_ssl.pfx -out root.pem -cacerts

If you want your file to be password protected etc, then there are additional options.

Another perspective for doing it on Linux... here is how to do it so that the resulting single file contains the decrypted private key so that something like HAProxy can use it without prompting you for passphrase.

openssl pkcs12 -in file.pfx -out file.pem -nodes

coudé !