When a document is shared with you by someone through the SigningHub for Word add-in, you will receive a notification email. Login into the SigningHub web to view and sign the shared document. See details how to sign a document.
1. Since the signatures are applied on a Word document, therefore you need to subscribe for an enterprise service plan that allows the "Office Signatures" provision.
2. It is recommended not to login the SigningHub for Word add-in on a signed document, as it will invalidate the existing signatures.