Hi, I've understood you perfectly, I have the same problem. We need include an external PDF exposed and reachable by HTTP to print in the same moment that user sends to print the invoice document and the delivery notes document (those two generated by SAP). The PDF is a legal document related to the customer generated by other system that has to be included in the shipping, so we need to print it consecutively to other two documents.
Did you found the solution for this?
Thanks!