Depending on your business needs, you can send a reminder to your recipient, if they haven't reviewed or signed the document.
This option is not available, if the document is completed.
Send a reminder on a sent document
Open the document and go to Recipients (found in the top right.) Find the recipient to send the reminder to and click on the name, then click on "Send Reminder."
The reminder feature is only for recipients that you have assigned a field to.
Reminder email example:
Review a reminder notification in Document Activity
When reminders are sent out, a notification will also show up in the Activity. Click the ellipses > Document info to access it.