One more question. We use a software that generates a personalized PDF. I need to add a string of text to the pdf indicating the order number. For the API call can I send the PDF URL so that we upload it to your server and then add a text field on top of it with the order number? Please note that this is not a standard template PDF. Each PDF that we would provide the URL to in the API call would be a unique PDF generated by another piece of software. I would be connecting these via Zapier.