Add a Text Watermark using Stamper on PDFTron UWP

Question

I have added a watermark to my pdf using the following code. My actual requirement is to display the watermark when the user tries to print the pdf. (print preview and the printed copy should have the watermark and not on the original doc on the viewer)

I set the flags ShowsOnScreen(false) and ShowsOnPrint(true) but it displays on the print preview but also display on the viewer as well. Another issue is this watermark can be selected and do other annotations like highlighting.

Please suggest me a workaround. Either I need to hide the watermark from the viewer and display only on print preview/print or Show me a way that watermark displays on the viewer as well but it has to be read-only.

using (Stamper st = new Stamper(StamperSizeType.e_relative_scale, 0.9, 0.9)) 
                { 
                    pdfDoc.InitSecurityHandler(); 

                    st.SetAlignment(StamperHorizontalAlignment.e_horizontal_center, StamperVerticalAlignment.e_vertical_center); 
                    st.SetFontColor(new ColorPt(0, 0, 0));                    st.SetOpacity(0.3); 
                    st.SetAsBackground(false); 
                    st.ShowsOnScreen(false); 

                    st.SetRotation(-45); 
                    st.ShowsOnPrint(true); 

                    st.SetAsAnnotation(false); 

                    st.StampText(pdfDoc, "If you are reading this\nthis is an even page", new PageSet(1, pdfDoc.GetPageCount())); 
                }

Answer 1

Got sorted with the help from PDFTron team. Here is the code

public async Task<PDFDoc> SetWatermark(PDFDoc pdfDoc)
    {
        try
        {
            #region Solution 1
            var text = "Sample Watermark\nSample Watermark";

            pdfDoc.InitSecurityHandler();
            Image img1 = null;

            // Create a dummy document
            using (PDFDoc tempDoc = new PDFDoc())
            using (Stamper st = new Stamper(StamperSizeType.e_relative_scale, 0.9, 0.9))
            {
        // Add a page to the dummy doc.
                tempDoc.PagePushBack(tempDoc.PageCreate());
                st.SetAlignment(StamperHorizontalAlignment.e_horizontal_center, StamperVerticalAlignment.e_vertical_center);

                // Set text color to black
                st.SetFontColor(new ColorPt(0, 0, 0));

                // Add a text to the dummy page. This text will be the watermark you going to apply on your original document.
                st.StampText(tempDoc, text, new PageSet(1, tempDoc.GetPageCount()));
        // Reduce PDF page to minimal size
                tempDoc.GetPage(1).SetMediaBox(tempDoc.GetPage(1).GetVisibleContentBox());

        // Require a sepaprate license
                PDFDraw draw = new PDFDraw();
                // Adjust image output quality
                draw.SetDPI(100);
                draw.SetPageTransparent(true);

                // Export the dummy page's text as an image
                var pngImageData = await draw.ExportAsStreamAsync(tempDoc.GetPage(1), "PNG");
                img1 = await Image.CreateAsync(pdfDoc.GetSDFDoc(), pngImageData);
            }

            // Create a new stamper to embed the above created image to the original doc
            using (Stamper st = new Stamper(StamperSizeType.e_relative_scale, 0.9, 0.9))
            {
                // Adjust final stamp positioning
                st.SetAlignment(StamperHorizontalAlignment.e_horizontal_center, StamperVerticalAlignment.e_vertical_center);
                st.SetOpacity(0.3);
                st.SetAsBackground(false);
                st.ShowsOnScreen(true);
                st.SetRotation(-45);
                st.ShowsOnPrint(true);
                st.SetAsAnnotation(false); //Make it true if you want to add this watermark to the XFDF file

                st.StampImage(pdfDoc, img1, new PageSet(1, pdfDoc.GetPageCount()));
            }
            #endregion
        }
        catch (Exception ex)
        {
            throw;
        }
        return pdfDoc; //Retrun the watermark embeded document
    }