To enhance the shopping experience of the customers and to increase the sales quantity store owners provide their customers many options like Cash on Delivery or Credit Purchase which gives the customers to make the payment once the order is delivered to them.

Overdue Invoice Automated Reminder extension will allow the admin to send reminder email informing to make the payment. It also allows admin to print unpaid invoices in PDF format or email it to the customer. The native Magento system will only email the invoice to the customer when you actually invoice the order which will mark the order as paid. But in the case of offline payment methods, you need to email the invoice to the customer for asking for payment or reminding him.