Google Drive is Google's file sync app that lets you store all of your files online alongside your Google Docs documents, and keep them synced with all of your devices.
File signed client agreements with their audit pages in client files.
Your final agreement folder holds the signed PDF and its audit certificate, and the owner gets links to both.
Send approved matter agreements for signature and return signer links.
Your signers get personal signature requests from the final agreement you email, and you get a reply with the invitation wording and their links.