Collaborators contribute to your Project; either helping you to write the document, to review the content of the document, or to provide their signatures to finalize the document.
In Documill Leap Salesforce app, collaborators can come from two sources:
A registered user in your Leap Organization.
A Salesforce Contact from the Account tied to your Salesforce Record.
When managing your collaborators, you can search from the above two sources by clicking this button: