How to programmatically add a custom stamp annotation when a user clicks on a PDF page?

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In the WPF PDF Viewer, custom stamp annotations can be programmatically added when a user clicks on a PDF page using the AddStamp API and with PageClicked event. This functionality is achieved by utilizing the CurrentPageIndex API to obtain the index of the current page displayed in the PdfViewerControl . Converting the point to pixels for the page point eliminates the need to acquire scroll coordinates from the page coordinate. Additionally, it’s recommended to use the the ZoomPercentage API to retrieve the current zoom percentage. This consideration is particularly important if the zoom percentage is not set to 100.

Steps to add custom stamp annotation when a user clicks on a PDF page in C#

The below steps illustrate how to add a custom stamp annotation when a user clicks on a PDF page.

Step 1: Create a customized button in MainWindow.xaml. This button is to enable the user to add custom stamp when clicking the page, by setting true value to the boolean “CanAddAnnotation”.

XAML

<Button x:Name="AddStamp" Content="Add Stamp" Width="75" Click="AddStamp_Click"/>

private void AddStamp_Click(object sender, RoutedEventArgs e)
{
  checkAddAnnotation = true;            
}

Step 2: Wire the PageClicked event in the constructor class of the main window.

public MainWindow()
{
   InitializeComponent();
   pdfViewer.Load("../../Data/F#.pdf");
   pdfViewer.PageClicked += PdfViewer_PageClicked;
}

Step 3: The added custom stamp annotation when the page is clicked.

To incorporate custom stamp annotations into the PDF viewer, it listens for a click event (PdfViewer_PageClicked) and verifies if the CanAddAnnotation flag is set to true. If affirmative, the code proceeds to include an annotation in the PDF.
Given that PDF pages are measured in point values while the click event returns pixel values, conversion from pixel point (args.Position) to page points (pagePoint) is necessary. This is achieved through the ConvertClientPointToPagePoint method provided by the pdfViewer.
A stamp annotation (PdfStampAnnotation) is created utilizing an image (ThankYou.png) loaded from a relative path, with the stamp’s dimensions set to 200x100 pixels.
Should the zoom percentage of the PDF viewer deviate from 100%, the code adjusts the annotation’s position based on the zoom factor to ensure accurate placement on the page.
Lastly, the code adds the stamp annotation to the PDF viewer at the calculated position on the specified page (pageNumber). It then sets CanAddAnnotation to false to prevent further annotation additions until the flag is reset.

private void PdfViewer_PageClicked(object sender, Syncfusion.Windows.PdfViewer.PageClickedEventArgs args)
{
   if(CanAddAnnotation)
   {
       PdfUnitConvertor convertor = new PdfUnitConvertor();
       Mouse.OverrideCursor = Cursors.Arrow;
       Point clientPoint = args.Position;
       //Retrieve the page number that corresponds to the client point
       int pageNumber = pdfViewer.CurrentPageIndex;

       //Retrieve the page point
       Point pagePoint = pdfViewer.ConvertClientPointToPagePoint(clientPoint, pageNumber);
       double x = pagePoint.X;
       double y = pagePoint.Y;
       x = convertor.ConvertToPixels((float)args.Position.X, PdfGraphicsUnit.Pixel);
       y = convertor.ConvertToPixels((float)args.Position.Y, PdfGraphicsUnit.Pixel);

       Point position = new Point(x, y);
       pdfViewer.AnnotationMode = PdfDocumentView.PdfViewerAnnotationMode.None;
       var bitmapImage = new BitmapImage(new Uri("../../Data/ThankYou.png", UriKind.RelativeOrAbsolute));
       bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
       var image = new System.Windows.Controls.Image() { Source = bitmapImage };
       var pdfStamp = new PdfStampAnnotation(image);
       if (pdfViewer.ZoomPercentage != 100)
       {
           float zoomFactor = (float)pdfViewer.ZoomPercentage / 100.0f;
           var x1 = position.X / zoomFactor;
           var y1 = position.Y / zoomFactor;
           position = new Point(x1, y1);
       }
       //Enter the required size of the stamp.
       System.Drawing.Size stampSize = new System.Drawing.Size(200, 100);
       pdfViewer.AddStamp(pdfStamp, pageNumber, position, stampSize);
       CanAddAnnotation = false;
   }          
}

A complete working sample to add a custom stamp annotation when a user clicks on a PDF page can be downloaded from GitHub.

The execution of the above code results in the addition of a custom stamp annotation when a user clicks on a PDF page, appearing as follows.

How to programmatically add a custom stamp annotation when a user clicks on a PDF page?

Steps to add custom stamp annotation when a user clicks on a PDF page in C#

See Also

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