GdPicture.NET的功能强大之处除了可实现文档显示，获取TWAIN扫描图像，进行图像处理，执行光学字符识别等功能外，也可以在文档中添加水印，下面是使用GdPicture.NET在PDF文件中添加水印的代码示例：

》》》下载GdPicture.NET试用版。

Const text As String = "WATERMARK"
        Const textSize As Integer = 100
        Const rotation As Single = 320 \'Note: rotation is anti-clockwise
        Const font As String = "Arial"

        Using gdPicturePDF As New GdPicturePDF
            gdPicturePDF.LoadFromFile("c:\input.pdf", False)
            gdPicturePDF.SetMeasurementUnit(PdfMeasurementUnit.PdfMeasurementUnitPoint)
            gdPicturePDF.SelectPage(1)
            Using gdpicturePDFBack As New GdPicturePDF
                gdpicturePDFBack.NewPDF()
                Dim pageWidth As Single = gdPicturePDF.GetPageWidth()
                Dim pageHeight As Single = gdPicturePDF.GetPageHeight()

                gdpicturePDFBack.ClonePage(gdPicturePDF, 1)

                gdPicturePDF.SetOrigin(PdfOrigin.PdfOriginTopLeft)
                gdPicturePDF.ClearPageContent()

                Dim fontResName As String = gdPicturePDF.AddTrueTypeFont(font, True, False, False)
                gdPicturePDF.SetTextSize(textSize)
                gdPicturePDF.DrawRotatedText(fontResName, 0, gdPicturePDF.GetTextHeight(fontResName, textSize), text, rotation)
                gdPicturePDF.SaveGraphicsState()
                gdPicturePDF.SetBlendMode(PdfBlendMode.PdfBlendModeNormal)
                gdPicturePDF.SetFillAlpha(200)

                Dim status As GdPictureStatus = gdPicturePDF.DrawPage(gdpicturePDFBack, 1, 0, pageHeight, pageWidth, pageHeight)

                gdPicturePDF.ResetGraphicsState()

                gdPicturePDF.SaveToFile("c:\output.pdf")
            End Using
        End Using