Markup text on PDF page using Text Markup Annotation in .NET

Blog category: PDF

February 02, 2021

PDF Text Markup annotation allows to markup text (highlight, strikeout, underline, squiggly underline) on PDF page.
VintaSoft PDF .NET Plug-in provides API, which allows to add programmatically a PDF Text Markup annotation onto PDF page.
Also the SDK provides the visual tool PdfTextMarkupTool, which allows to markup text visually using PDF Text Markup annotation on PDF page displayed in WinForms or WPF image viewer. Added annotations are fully compatible with any PDF viewer compliant with PDF specification.


Here is C# code that demonstrates how to markup text programmatically (highlight, strikeout, underline, squiggly underline) on PDF page using PDF Text Markup annotation:
/// <summary>
/// Highlights specified text in PDF document.
/// </summary>
/// <param name="inputPdfFilename">The input PDF filename.</param>
/// <param name="outputPdfFilename">The output PDF filename.</param>
/// <param name="text">A text that must be highlighted.</param>
public static void HiglightTextInPdfDocument(string inputPdfFilename, string outputPdfFilename, string text)
{
    MarkupTextInPdfDocument(inputPdfFilename, outputPdfFilename, 
        Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationType.Highlight, System.Drawing.Color.Orange, text);
}

/// <summary>
/// Strikeouts specified text in PDF document.
/// </summary>
/// <param name="inputPdfFilename">The input PDF filename.</param>
/// <param name="outputPdfFilename">The output PDF filename.</param>
/// <param name="text">A text that must be striked out.</param>
public static void StrikeoutTextInPdfDocument(string inputPdfFilename, string outputPdfFilename, string text)
{
    MarkupTextInPdfDocument(inputPdfFilename, outputPdfFilename, 
        Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationType.StrikeOut, System.Drawing.Color.Red, text);
}

/// <summary>
/// Underlines specified text in PDF document.
/// </summary>
/// <param name="inputPdfFilename">The input PDF filename.</param>
/// <param name="outputPdfFilename">The output PDF filename.</param>
/// <param name="text">A text that must be underlined.</param>
public static void UnderlineTextInPdfDocument(string inputPdfFilename, string outputPdfFilename, string text)
{
    MarkupTextInPdfDocument(inputPdfFilename, outputPdfFilename, 
        Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationType.Underline, System.Drawing.Color.Green, text);
}

/// <summary>
/// Squiggly undelines specified text in PDF document.
/// </summary>
/// <param name="inputPdfFilename">The input PDF filename.</param>
/// <param name="outputPdfFilename">The output PDF filename.</param>
/// <param name="text">A text that must be squiggly underlined.</param>
public static void SquigglyUnderlineTextInPdfDocument(string inputPdfFilename, string outputPdfFilename, string text)
{
    MarkupTextInPdfDocument(inputPdfFilename, outputPdfFilename, 
        Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationType.Squiggly, System.Drawing.Color.Blue, text);
}

/// <summary>
/// Markups specified text in PDF document.
/// </summary>
/// <param name="inputPdfFilename">The input PDF filename.</param>
/// <param name="outputPdfFilename">The output PDF filename.</param>
/// <param name="color">The markup annotation color.</param>
/// <param name="annotationType">The markup annotation type.</param>
/// <param name="text">A text to markup.</param>
private static void MarkupTextInPdfDocument(
    string inputPdfFilename,
    string outputPdfFilename,
    Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationType annotationType,
    System.Drawing.Color color,
    string text)
{
    // open input PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = new Vintasoft.Imaging.Pdf.PdfDocument(inputPdfFilename))
    {
        // for each PDF page
        foreach (Vintasoft.Imaging.Pdf.Tree.PdfPage page in document.Pages)
        {
            // extract text region of PDF page
            Vintasoft.Imaging.Text.TextRegion pageTextRegion = page.ExtractTextRegion(false);

            // search and markup all specified text on PDF page
            int index = 0;
            Vintasoft.Imaging.Text.TextRegion foundText;
            while (true)
            {
                // find next text
                foundText = pageTextRegion.FindText(text, ref index, false);
                if (foundText == null)
                    break;
                index += foundText.Symbols.Length;

                // markup found text
                MarkupText(page, foundText, annotationType, color);
            }
        }

        // save PDF document to output file
        document.SaveChanges(outputPdfFilename);
    }
}

/// <summary>
/// Markups specified text region in PDF page.
/// </summary>
/// <param name="page">The page.</param>
/// <param name="textRegion">The text region to markup.</param>
/// <param name="color">The markup annotation color.</param>
/// <param name="annotationType">The markup annotation type.</param>
private static void MarkupText(
    Vintasoft.Imaging.Pdf.Tree.PdfPage page,
    Vintasoft.Imaging.Text.TextRegion textRegion,
    Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationType annotationType,
    System.Drawing.Color color)
{
    // create markup annotation of specified type
    Vintasoft.Imaging.Pdf.Tree.Annotations.PdfTextMarkupAnnotation markupAnnotation =
        new Vintasoft.Imaging.Pdf.Tree.Annotations.PdfTextMarkupAnnotation(page, annotationType);

    // set annotation properties
    markupAnnotation.SetTextRegion(textRegion);
    markupAnnotation.Color = color;
    markupAnnotation.Title = System.Environment.UserName;
    markupAnnotation.CreationDate = System.DateTime.Now;

    // generate annotation appearance
    markupAnnotation.UpdateAppearance();

    // add annotation to annotations of PDF page
    if (page.Annotations == null)
        page.Annotations = new Vintasoft.Imaging.Pdf.Tree.Annotations.PdfAnnotationList(page.Document);
    page.Annotations.Add(markupAnnotation);
}


Here is C# code that demonstrates how to markup text visually on PDF page displayed in WinForms image viewer:
/// <summary>
/// Sets the PdfTextMarkupTool as current visual tool in specified image viewer.
/// </summary>
/// <param name="imageViewer">The image viewer.</param>
public static void SetPdfTextMarkupTool(Vintasoft.Imaging.UI.ImageViewer imageViewer)
{
    // create an instance of the PdfTextMarkupTool class
    Vintasoft.Imaging.Pdf.UI.PdfTextMarkupTool textMarkupTool = new Vintasoft.Imaging.Pdf.UI.PdfTextMarkupTool();

    // set text markup mode to "Highlight"
    textMarkupTool.MarkupMode = Vintasoft.Imaging.Pdf.UI.PdfTextMarkupToolMode.Highlight;

    // set color of markup annotation to "Orange"
    textMarkupTool.HighlightColor = System.Drawing.Color.Orange;

    // subscribe to the MarkupAnnotationCreated event
    textMarkupTool.MarkupAnnotationCreated += TextMarkupTool_MarkupAnnotationCreated;

    // get TextSelectionTool from image viewer
    Vintasoft.Imaging.UI.VisualTools.TextSelectionTool textSelectionTool = GetTextSelectionTool(imageViewer);

    // set the PdfTextMarkupTool+TextSelectionTool as visual tool of the image viewer
    imageViewer.VisualTool = new Vintasoft.Imaging.UI.VisualTools.CompositeVisualTool(textMarkupTool, textSelectionTool);
}

/// <summary>
/// Returns the text selection tool for specified image viewer.
/// </summary>
/// <param name="imageViewer">The image viewer.</param>
/// <returns>The text selection tool.</returns>
private static Vintasoft.Imaging.UI.VisualTools.TextSelectionTool GetTextSelectionTool(Vintasoft.Imaging.UI.ImageViewer imageViewer)
{
    // search a TextSelectionTool in visual tools of the image viewer
    Vintasoft.Imaging.UI.VisualTools.TextSelectionTool textSelectionTool =
        Vintasoft.Imaging.UI.VisualTools.VisualTool.FindVisualTool<Vintasoft.Imaging.UI.VisualTools.TextSelectionTool>(imageViewer.VisualTool);
    if (textSelectionTool != null)
        return textSelectionTool;

    // create an instance of text selection tool
    return new Vintasoft.Imaging.UI.VisualTools.TextSelectionTool();
}

/// <summary>
/// Handles the MarkupAnnotationCreated event of the PdfTextMarkupTool visual tool.
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">The <see cref="Vintasoft.Imaging.Pdf.UI.PdfTextMarkupAnnotationEventArgs" /> instance containing the event data.</param>
private static void TextMarkupTool_MarkupAnnotationCreated(object sender, Vintasoft.Imaging.Pdf.UI.PdfTextMarkupAnnotationEventArgs e)
{
    // set user name as title of text markup annotation
    e.MarkupAnnotation.Title = System.Environment.UserName;
}



Also VintaSoft Imaging .NET SDK installation package includes PDF Editor Demo and WPF PDF Editor Demo application, which allows to test the text markup feature (highlight, strikeout, underline, squiggly underline) on PDF page without any coding.

To highlight and markup text using toolbar in Vintasoft PDF Editor Demo is necessary:
Here is a screenshot demonstrating how to select and markup text on PDF page using the toolbox of Vintasoft PDF Editor Demo: Vintasoft PDF Editor Demo: Select and markup text on PDF page using toolbox



To markup selected text using context menu in Vintasoft PDF Editor Demo is necessary:
Here is a screenshot demonstrating how to markup selected text on PDF page using context menu of Vintasoft PDF Editor Demo: Vintasoft PDF Editor Demo: Markup selected text on PDF page using context menu


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