Saving pdf attachment is no different from saving any attachments. You could start with this code:
MailMessage mm = new MailMessage();
// load the message or download it from server
// save the first attachment
If you have trouble saving the pdf attachment, would it be possible to zip the original email and then send the zip archive to email@example.com along with the version of Rebex components that you are using?
It will enable us to check whether it is a problem with the component or with the email itself.