You can attach the file as a pdf to have trustfax send the pdf as a fax. You will need to make sure that the security identifiers are in the body of the email to ensure it is faxed from the proper account. If the identifiers are not in the body of the email or does not match an account, the fax will not be sent. You receive a reply from trustfax of the error.
here is a link on how to form the email properly:
http://www.trustfax.com/guides/tf/tf_send.html#send_email