Once you have sent a document to your customer, you can monitor it for clicks and opens, as well viewing and sending direct messaging. Just go to the envelope on the top right of you screen;
In this example, the 4 displayed next to the envelope, refers to the total amount of messages that the been exchanged;
When you click on it, this will reveal the trail of messages along with quite a lot of other information;
Customer Messaging
When you send a new message to a customer they will be able to view this as an email. To see the trail of messages, they will need to go into their document, click Messages on the top right;