Salesforce - Add Files from the files on the Opportunity?

How does Adobe pull files on an Opportunity into the agreement? 

We currently create a bunch of word documents and save them to the files section of the opportunity.  I want to be able see just those files specific to that Opportunity.  Currently when I click Send Agreement for Signature and  "Add Files" it gives me ALL the files in Salesforce?  I just want the files that are from the Files Related List?