Audit trail of who has been sent documents


We are in the middle of creating a document management platform & policy. We are working on a highly confidential project and must have an audit history on who has been sent what documents, and when. We would like our workflow to look like this:
Employee asks for approval to send documents to a specific person/company
Manager approves that request
Document is sent via smartsheet - with an audit trail

I know I can set up the form to request to send, and have the manager approve the form. However I am getting stumped on how to create an audit trail of who has been sent the document. I thought there would be an audit history on each row, but doesn't appear to be. Doesn't look like "sending" a file is something that is tracked on the activity log. Any ideas?