You can make it more convenient for your customers to pay their invoices by adding a clickable Pay Now button to your invoices. When clicked the link can launch a web page that is prefilled with the correct information ready for them to pay using an online payment system. See an example of a PDF that does this using the PayPal button here.
The pdfMachine ultimate parameter parsing feature allows you to easily insert images that will launch a url when clicked. More information >>>