Archive invoices, file signed agreements, sort project files. Every one is ready to run, and you can adjust it in plain language.
Place signer fields on final matter agreements.
Your final agreements reach the signers you list, and you get a reply with the invitation details in the original email thread.
Add signing proof to executed client agreements.
Keep signed agreements ready for handoff, with signature certificates or audit trails beside them and a clear note when proof is missing.