create online contract add-on for wordpress multisite

Hello, Goal is to create a contract tab in a project manager where inside admin has possibility to manage, create/write an on online contract or choose among a list of templates and just edit some stuff. Admin can save draft, edit after or save definetely and send automatically an email to client(s) registered for this project to ask coming see and sign contract online or offline. In fact, contract must be either print in PDF by client and sign “offline” and after can be uploaded and store in the file tab (but with restriction access; see below) and with a link to remind and open on contract tab or sign online with manual signature recognised (like a draw) and date automatically added. Once signed and approved by client (both way), contract must be locked and convert in PDF and impossible to modify. Possibility to create and have several contracts in contract tab (stored by title, date). Of course, link to contract signed must be stored and easily accessible to download anytime. Must be multisite comptatible with subsite and separation per project (client can only see their own project, so must keep this function) in each subsite. Only admin and client user role can see the tab and contract file. Global settings of project must allow : admin, only, to write or paste a template with a title admin to customize email to send to warn client Must be very lighweight, no useless code. And do not create a new plugin. Modify existing project manager plugin or one of the add-on. I have already a simple plugin like this to help you(but not organised per project) but not MU compatible. But could be useful for the manual signature recognised function and PDF function. Must be responsive for any devices as WP is currently. Please only answer if sure to be able to do.