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Highlight Form Fields in RadPdfViewer

Product Version Product Author
2019.1.117 RadPdfViewer for WinForms Dimitar


This article demonstrates how you can use the custom painting functionality in order to highlight the editable fields in PDF document.


1. Subscribe to the DocumentLoaded event. This event will allow you to access the pages of the document ans subscribe to their ElementPainted event.

private void RadPdfViewer1_DocumentLoaded(object sender, EventArgs e)
    foreach (var page in radPdfViewer1.PdfViewerElement.ViewElement.Children)
        page.ElementPainted += PdfViewerElement_ElementPainted;

Private Sub RadPdfViewer1_DocumentLoaded(ByVal sender As Object, ByVal e As EventArgs)
    For Each page In radPdfViewer1.PdfViewerElement.ViewElement.Children
        page.ElementPainted += PdfViewerElement_ElementPainted
    Next page

End Sub

2. Use the ElementPainted event to paint the border. You will need to consider the scroll and the zoom as well. Here is the code:

private void PdfViewerElement_ElementPainted(object sender, PaintEventArgs e)

    RadFixedPageElement p = sender as RadFixedPageElement;
    foreach (var item in p.Page.Annotations)
        e.Graphics.TranslateTransform(p.Transform.DX, p.Transform.DY);

        var zoom = radPdfViewer1.PdfViewerElement.ScaleFactor;
        e.Graphics.DrawRectangle(new Pen(Color.Yellow, 4), (int)(item.Rect.X * zoom), (int)(item.Rect.Y * zoom), (int)(item.Rect.Width * zoom), (int)(item.Rect.Height));

        e.Graphics.TranslateTransform(-p.Transform.DX, -p.Transform.DY);

Private Sub PdfViewerElement_ElementPainted(ByVal sender As Object, ByVal e As PaintEventArgs)

    Dim p As RadFixedPageElement = TryCast(sender, RadFixedPageElement)
    For Each item In p.Page.Annotations
        e.Graphics.TranslateTransform(p.Transform.DX, p.Transform.DY)

        Dim zoom = radPdfViewer1.PdfViewerElement.ScaleFactor
        e.Graphics.DrawRectangle(New Pen(Color.Yellow, 4), CInt(Fix(item.Rect.X * zoom)), CInt(Fix(item.Rect.Y * zoom)), CInt(Fix(item.Rect.Width * zoom)), CInt(Fix(item.Rect.Height)))

        e.Graphics.TranslateTransform(-p.Transform.DX, -p.Transform.DY)
    Next item
End Sub

This example will paint a yellow border around each field.

pdfviewer-highlight-form-fields 001


  • In a .NET Framework project, a reference to WindowsBase is required to be added:

pdfviewer-highlight-form-fields 002

  • In a .NET Core (or newer version), it is necessary to edit the proj file and include WPF:

pdfviewer-highlight-form-fields 003

pdfviewer-highlight-form-fields 004

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