[Exim] PEM vs x.509 certs in smtp over ssl

I have made the PEM files for courier impd-ssl and the system runs like
a champ!!! Can these same PEM's be used for exim smtp over ssl? If so,
how ?

I have had no luck finding out what a PEM is vs an x.509 cert.

Could someone point out a URL? Does anyone know how to make a PEM for
courier with Java <either a small program or keytool would do> I tired
an exported x.509 that was self certified with keytool - courier bawked
at it.

TIA