I'd like to know how to make attachments automatically open up at the end of the form and be included in the page numbering. Is there any way of inserting them in a subform or something of that nature? Thanks.
There are lots of ways, Paul presented the best of them.
What you want to do isn't near the standard signed document workflow.
Non-repudiation and changes apart, a Digital Signature represents a sign of acceptance of the content of the document. You not only want to change that content was well was the layout and visual of the document by appending / inserting new PDF.
Even if you could get it to work, in a few months/years, when someone tried to validate todays documents, chances are, they won't be able to.
As far as Signed documents go, try to follow Adobe's recomendations.
IMHO you should re-think your workflow to something that is similar to: