Answer
PDF Inserts are set up through Report Rules: there's a dedicated screen specifically for importing the PDF files you want available as inserts, and then you create a new Report Rule with an action configured to attach one or more of those imported PDFs to the report's output. The specific Report Rule Action Type used for this differs between Apps9 and Apps10, so check the documentation or Report Rule action-type options for your specific version rather than assuming the exact same action type name applies across both.