Personalized video greeting
Add the ability to record a video before sending the contract. Youtube etc should not be needed, use the webcam on the computer and record directly. It should be shown to the recipient when the document is opened and NOT be a part of the contract itself. This is a great way to do a personalized experience to a customer. Like "Hi xyz, Here is the document we talked about earlier today. Hope your round of golf will be great this afternoon.". A good way of increasing closing rate.
Or how about audio as well? So that an audio voiceover "explainer" could be listened to while reviewing a document