The PdfExportRenderer class gives you access to the exported document and provides you with the ability to change it before it is saved.
The PdfExportRenderer API gives you the ability to manipulate the document. The following two events are giving you the ability to make some final changes:
PageExported: occurs when each page is exported. The PageExportedEventArgs object gives you access to the editor which you can use to paint on the page.
PdfExporting: occurs before the export process is completed. This event gives you access to the exported document and at this point you can manipulate it using the PdfProcessing Library