If a customer signs a document, I would like to gain some extra information from this customer. For instance by providing some fields the customer has to fill or select an option before signing (so mandatory). For example I need to know if this customer wants to be billed monthly or annually but only when the customer agrees and signs, so only then I would like an option for the customer to select one of these options. Is it therefore possible to provide some extra pop-up fields eg when the customer clicks on the signing button?