Too Long; Didn't Read
The Virtru SDK is designed to build add-ons to extend Google Sheets, Docs, & Slides. It's designed to do exactly what I ultimately want to do. The code runs directly within G Suite, so it will support Virtru’s browser JS SDK. To build a Google Docs add-on that will allow me to generate a secure, encrypted copy of my Docs content and share it privately with authorized users. The only new functionality I need to add is to encrypt the document and apply my access controls.