Joe,
I have two solutions for you.
- First
If you click forward button and then open attached file and edit it, then
save changes - and only then, click Send Button, you will send that updated
file.
But in this case, edited files will be only stored as attachments in Send
Items folder (i.e. you will not have a copy of that file on HDD).
- Second solution is Attachments Processor for Outlook.
http://www.mapilab.com/outlook/attachments_processor/
You can setup a rule for this outlook plug-in to extract incoming
attachments to HDD, after that you can open extracted file from the link to
it in your incoming message, edit it, and use add-in option "Forward with
Attachments Processor for Outlook" for forwarding updated file.