This sample shows how to apply PDF watermarks and backgrounds in C# or VB.NET application.
Use the PdfDocument.CreateXObject method to add a PdfXObject object to your document. Use the new object for a watermark. You can set up the PDF watermark appearance using methods and properties of the object’s canvas. To access the canvas, use the PdfXObject.Canvas property.
The PdfCanvas.DrawXObject methods apply the watermark to a page. It’s ok to apply the same watermark to more than one page.
To convert a watermark to a background, set the DrawOnBackground property of the created object to true. After that, use apply the background to one or more pages using one of the PdfCanvas.DrawXObject methods.