Hi Darrin,
Thank you for replying us with the requirements.
As mentioned in our previous update, at present we do not have any event to track the document closing action in the PDF Viewer. We have planned to implement this event for 2019 Volume 1 release which is expected to be available in the month of March, 2019. In case if you require the feature immediately, please create a support incident using Direct Trac, so that we can deliver the patch for this event implementation.
Regards,
Ayswarya