Microsoft Outlook – e-mail rules

I would like to talk to someone who really knows outlook e-mail and how it works with attachments. The basic process I would like to use is for approval of purchase orders. I have a document, must be a .pdf file, to e-mail for approval to pay. the document is copied and pasted to the e-mail so it is viewable for the recepient.They would reply back an approval and I need the document to come back so I know which one they are approving. Is there a way to force the recepient to forward the message & not reply so the document comes back?