Routing

I am using the MS routing wizard. When a custom form gets saved to a public folder a copy (email attachment) of it gets sent to each person on the route. When each user opens the attachment (custom form) I want them to be able to save their changes over top of the original form in the public folder. Only one person at a time gets the attachment. so there is no chance of two people opening it at the same time and one overwriting the others changes. So I am stuck on coding how to go about saving the attachment back to the public folder.

Thanks for the help.