replied on January 9, 2014
Is your use case that you want to completely fill out the form for them so it's identical to what it was last time they submitted, but they need to revise the attachment and reattach it?
Based on your level of expertise around here, you may already know how to build the URL to fill out the fields on the form:
add ?parametername=value¶meter2name=value¶meter3name=value etc. to the end of the URL used to access the form. This will only fill out text, number and pull down fields. It will not fill in fields that are part of a repeatable Collection.
I don't know of functionality to automatically attach something to a form.