How to add a highlight text markup annotation after selecting text in the WPF PDF Viewer Control?

In the WPF PDF Viewer, to add a highlight text markup annotation for the selected text, it can be achieved by utilizing the TextSelectionCompleted event of the PDF viewer. Once the selection of text in the PDF viewer is complete, the event handler triggers and retrieves the selected text, page index, and associated rectangular bounds information. If text is selected across multiple pages, it iterates through each selected text to obtain the bounds value and page number. After that, a text markup annotation is created, passing the rectangular bounds, and configured with attributes such as color and type. Finally, the annotation is added to the corresponding page in the loaded PDF document.

Steps to add highlight text markup annotation after selecting the text in WPF PDF Viewer Control

Step 1: Wire the TextSelectionCompleted event in the constructor class of the main window.

C#

pdfViewer.TextSelectionCompleted += PdfViewer_TextSelectionCompleted;

Step 2: Highlight text after selecting it in the WPF PDF Viewer Control using C#.

• The event handler is triggered when the user completes selecting the text in the PDF document. Using TextSelectionCompletedEventArgs, retrieve the selected text as a string using args.SelectedText.
• Then, args.SelectedTextInformation is a dictionary which provides information about text selections. The page index serves as the key, with a collection of text and its bounding information as the value.
• The collection of texts with their bounding information is also a dictionary object. It contains string keys representing the text and rectangle bounds as their corresponding values.
• Iterate through this dictionary to retrieve the rectangular bounds values stored within it.
• Next, create a new PdfTextMarkupAnnotationobject and pass the rectangular bounds value, effectively adding a highlight annotation to the PDF document.
• Set the annotation properties such as color and type, specifying it as ‘Highlight’.
• Finally, add the PdfTextMarkupAnnotation to the desired page in the LoadedDocument property of the PdfViewer. This will reflect in the PdfViewer control without the need to reload the document.

C#

private void PdfViewer_TextSelectionCompleted(object sender, TextSelectionCompletedEventArgs args)
{
   //Get the whole selected text 
   string selectedText = args.SelectedText;

   PdfLoadedDocument loadedDocument = pdfViewer.LoadedDocument;

   //Get the selected text and its rectangular bounds for each page separately if the selection is made on multiple pages 
   Dictionary<int, Dictionary<string, System.Drawing.Rectangle>> selectedTextInformation = args.SelectedTextInformation;
   
   foreach (var SelectedValue in selectedTextInformation)
   {
       int pageIndex = SelectedValue.Key;

       Dictionary<string, System.Drawing.Rectangle> innerDictionary = SelectedValue.Value;

       foreach (var innerValue in innerDictionary)
       {
           string innerKey = innerValue.Key;
           RectangleF rect = new RectangleF(innerValue.Value.X, innerValue.Value.Y, innerValue.Value.Width, innerValue.Value.Height);

           PdfTextMarkupAnnotation markupAnnotation = new PdfTextMarkupAnnotation(rect);
           markupAnnotation.TextMarkupColor = new PdfColor(System.Drawing.Color.Red);
           markupAnnotation.TextMarkupAnnotationType = PdfTextMarkupAnnotationType.Highlight;
           loadedDocument.Pages[pageIndex - 1].Annotations.Add(markupAnnotation);
       }
   }
}

A complete working sample to add a highlight text markup annotation after selecting text in WPF PDF Viewer Control can be downloaded from GitHub.

The execution of the above code results in the add a highlight text markup annotation after selecting text in WPF PDF Viewer Control, appearing as follows.

Conclusion

I hope you enjoyed learning about how to add a highlight text markup annotation after selecting text in the WPF PDF Viewer Control.

You can refer to our WPF PDF Viewer page to know about its other groundbreaking feature representations and documentation, and how to quickly get started for configuration specifications.

For current customers, you can check out our components from the License and Downloads page. If you are new to Syncfusion, you can try our 30-day free trial to check out our other controls.

If you have any queries or require clarifications, please let us know in the comments section below. You can also contact us through our support forums, Direct-Trac, or feedback portal. We are always happy to assist you!