Create stringer audit trial using docusign or equivalent to electronically check

General information for the business: We are a business selling power conversion units to blue chip customers
Kind of development: Customization of existing program
Description of every module: We need to use docusign or some other basic package allowing legally binding signatures to accept our sales order acknowledgments, Purchase orders, contracts, drawings etc etc.
Description of requirements/functionality: We need it to populate a standard document using mail merger, which already exists, and then allow for us to track, for our customers to sign and to save this within our system
OS requirements: Windows, Mac OS
Extra notes: We flip between windows and Mac. Happy for this to be done within a windows environment