If you want to start interchanging electronic relevant in law documents with your contractor via Diadoc, you shall sign no additional contracts: at connection stage all participants of electronic document flow sign statement on accession to Rules, stating that the participant agrees to admit e-documents signed with digital e-signature as equal to paper documents with handwritten signature.
If you want to agree forms and types of interchanged documents with your contractor then you can enter to an agreement thereon.