How to Add Overlay/Underlay Stamps to PDF?

Question

Once i create the some stamp(watermarks), i need with options such as overlay, underlay, how can i do this?

Launching the application: A-PDF Watermark
In the main window, clicking "add image watermark" icon, then will open the New Image Watermark configuration window, you can set the desired options for the image watermark here, where you can mark the "As background" value as true(Underlay) or false(Overlay).
Return to the main window, clicking "File" menu, then select "Add PDF Document" item, Add PDF(s) which you want to add watermark
In the watermark list window, marking the image-Overlay/Underlay watermark item as checked
Clicking "Watermark" button to add the image-Overlay/Underlay watermark