Triggers are CRM automation tools. They can track customers actions and some changes in CRM: order payments, filling out CRM forms or calls. Your employees no longer have to go into each deal and check if the customer has read your email or paid the bill. Triggers will see the changes and automatically change the stage of the item.
Document opened trigger will help you to automate work with invoices and quotes. It is triggered when the client opens a public link to the document.
Here's a typical scenario: a manager should send an invoice or a quote to a client. With the trigger help, the manager can call the client when he or she opens the document.
Find out more about how to use this trigger in this help article