PdfArtifactWatermarkOptions

public sealed class PdfArtifactWatermarkOptions : PdfWatermarkOptions

PdfLoadOptions loadOptions = new PdfLoadOptions();
using (Watermarker watermarker = new Watermarker(@"D:\test.pdf", loadOptions))
{
    using (ImageWatermark watermark = new ImageWatermark(@"D:\icon.png"))
    {
        watermark.HorizontalAlignment = HorizontalAlignment.Right;
        watermark.VerticalAlignment = VerticalAlignment.Bottom;

        PdfArtifactWatermarkOptions options = new PdfArtifactWatermarkOptions();
        options.PageIndex = -1; // डिफ़ॉल्ट - सभी पृष्ठ

        watermarker.Add(watermark, options);
        watermarker.Save();
    }
}