[stunnel-users] Which X.509 certificate types (.crt, .pem, .der .p7c) possible for stunnel and how to import them?

Which X.509 certificate types (e.g. .crt, .pem, .der .p7c) are possible for stunnel? Assume I have got such a certificate as separate file (and not retrieved by OpenSSL). How do I import it into stunnel? Do I have to just copy it into (which ?) directory? Does the certifcate file name have to have a certain pattern? Or is stunnel smart enough to read and analyze the content independently from filename? Thank you Ben