The outstanding invoices report is a handy way to grab a list of all open invoices (for all patients) at any given time. You'll also be able to print or email invoices directly from that report!
To do that, just select the "Actions" button, which will be on the right side of the report. You'll have the option to print, email to the patient, or email to an other third party (if you've added an additional email address to the patient's details):
Keep in mind that the outstanding invoices report can't be filtered by patient—it will show all patients' invoices for the dates, businesses, and practitioners in question. If you need to generate a summary of outstanding invoices for an invidual patient, creating an account statement will be a good place to start!