PDF Highlight Annotation using C#

Text Markup Annotations shall appear as highlights, underlines, strikeouts, or jagged (“squiggly”) underlines in the text of a document. When opened, they shall display a pop-up window containing the text of the associated note.

The properties of the text markup annotations in the PDF document can be edited using the properties window provided in the PDF viewer control. The color, opacity, author, and subject of the text markup annotation can be modified.

Its is possible to get or set the settings of the highlight annotations using the highlightSettings property. The highlightSettings property is used to set the color, opacity, author, subject, modifiedDate and isLocked properties of the highlight annotations.

Also possible to get or set the settings of the strikethrough annotations using the strikethroughSettings property. The strikethroughSettings property is used to set the color, opacity, author, subject, modifiedDate, and isLocked properties of the strikethrough annotations.

The next feature is the ability to get or set the settings of the underline annotations using the underlineSettings property. The underlineSettings property is used to set the color, opacity, author, subject, modifiedDate, and isLocked properties of the underline annotations.

The following code snippet also work with Aspose.PDF.Drawing library.

Add Text Markup Annotation

In order to add an Text Markup Annotation to the PDF document, we need to perform the following actions:

  1. Load the PDF file - new Document object.
  2. Create annotations:
  3. After we should add all annotations to the page.
// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void AddTextMarkupAnnotations()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Annotations();

    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "sample.pdf"))
    {
        // Create a TextFragmentAbsorber to find the text "PDF"
        var tfa = new Aspose.Pdf.Text.TextFragmentAbsorber("PDF");
        tfa.Visit(document.Pages[1]);

        // Create annotations for the found text fragments
        var highlightAnnotation = new Aspose.Pdf.Annotations.HighlightAnnotation(document.Pages[1], tfa.TextFragments[1].Rectangle)
        {
            Title = "Aspose User",
            Color = Aspose.Pdf.Color.LightGreen
        };

        var strikeOutAnnotation = new Aspose.Pdf.Annotations.StrikeOutAnnotation(document.Pages[1], tfa.TextFragments[2].Rectangle)
        {
            Title = "Aspose User",
            Color = Aspose.Pdf.Color.Blue
        };

        var squigglyAnnotation = new Aspose.Pdf.Annotations.SquigglyAnnotation(document.Pages[1], tfa.TextFragments[3].Rectangle)
        {
            Title = "Aspose User",
            Color = Aspose.Pdf.Color.Red
        };

        var underlineAnnotation = new Aspose.Pdf.Annotations.UnderlineAnnotation(document.Pages[1], tfa.TextFragments[4].Rectangle)
        {
            Title = "Aspose User",
            Color = Aspose.Pdf.Color.Violet
        };

        // Add annotations to the page
        document.Pages[1].Annotations.Add(highlightAnnotation);
        document.Pages[1].Annotations.Add(squigglyAnnotation);
        document.Pages[1].Annotations.Add(strikeOutAnnotation);
        document.Pages[1].Annotations.Add(underlineAnnotation);

        // Save PDF document
        document.Save(dataDir + "AddTextMarkupAnnotations_out.pdf");
    }
}

If you want to highlight a multi-line fragment you should use advanced example:

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void AddHighlightAnnotationAdvanced()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Annotations();

    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "sample_mod.pdf"))
    {
        var page = document.Pages[1];
        var tfa = new TextFragmentAbsorber(@"Adobe\W+Acrobat\W+Reader", new TextSearchOptions(true));
        tfa.Visit(page);
        foreach (var textFragment in tfa.TextFragments)
        {
            var highlightAnnotation = HighLightTextFragment(page, textFragment, Color.Yellow);
            page.Annotations.Add(highlightAnnotation);
        }

        // Save PDF document
        document.Save(dataDir + "AddHighlightAnnotationAdvanced_out.pdf");
    }
}

private static HighlightAnnotation HighLightTextFragment(Page page,
    Aspose.Pdf.Text.TextFragment textFragment, Aspose.Pdf.Color color)
{
    if (textFragment.Segments.Count == 1)
    {
        return new Aspose.Pdf.Annotations.HighlightAnnotation(page, textFragment.Segments[1].Rectangle)
        {
            Title = "Aspose User",
            Color = color,
            Modified = DateTime.Now,
            QuadPoints = new Aspose.Pdf.Point[]
            {
                new Aspose.Pdf.Point(textFragment.Segments[1].Rectangle.LLX, textFragment.Segments[1].Rectangle.URY),
                new Aspose.Pdf.Point(textFragment.Segments[1].Rectangle.URX, textFragment.Segments[1].Rectangle.URY),
                new Aspose.Pdf.Point(textFragment.Segments[1].Rectangle.LLX, textFragment.Segments[1].Rectangle.LLY),
                new Aspose.Pdf.Point(textFragment.Segments[1].Rectangle.URX, textFragment.Segments[1].Rectangle.LLY)
            }
        };
    }

    var offset = 0;
    var quadPoints = new Aspose.Pdf.Point[textFragment.Segments.Count * 4];
    foreach (Aspose.Pdf.Text.TextSegment segment in textFragment.Segments)
    {
        quadPoints[offset + 0] = new Aspose.Pdf.Point(segment.Rectangle.LLX, segment.Rectangle.URY);
        quadPoints[offset + 1] = new Aspose.Pdf.Point(segment.Rectangle.URX, segment.Rectangle.URY);
        quadPoints[offset + 2] = new Aspose.Pdf.Point(segment.Rectangle.LLX, segment.Rectangle.LLY);
        quadPoints[offset + 3] = new Aspose.Pdf.Point(segment.Rectangle.URX, segment.Rectangle.LLY);
        offset += 4;
    }

    var llx = quadPoints.Min(pt => pt.X);
    var lly = quadPoints.Min(pt => pt.Y);
    var urx = quadPoints.Max(pt => pt.X);
    var ury = quadPoints.Max(pt => pt.Y);
    return new Aspose.Pdf.Annotations.HighlightAnnotation(page, new Aspose.Pdf.Rectangle(llx, lly, urx, ury))
    {
        Title = "Aspose User",
        Color = color,
        Modified = DateTime.Now,
        QuadPoints = quadPoints
    };
}

private static void GetHighlightedText()
{
    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "sample_mod.pdf"))
    {
        var highlightAnnotations = document.Pages[1].Annotations
            .Where(a => a.AnnotationType == Aspose.Pdf.Annotations.AnnotationType.Highlight)
            .Cast<Aspose.Pdf.Annotations.HighlightAnnotation>();
        foreach (var ta in highlightAnnotations)
        {
            Console.WriteLine($"[{ta.GetMarkedText()}]");
        }
    }
}

Get Text Markup Annotation

Please try using the following code snippet to Get Text Markup Annotation from PDF document.

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void GetTextMarkupAnnotation()
{
    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "sample_mod.pdf"))
    {
        var textMarkupAnnotations = document.Pages[1].Annotations
            .Where(a => a.AnnotationType == Aspose.Pdf.Annotations.AnnotationType.Highlight
            || a.AnnotationType == Aspose.Pdf.Annotations.AnnotationType.Squiggly)
            .Cast<Aspose.Pdf.Annotations.TextMarkupAnnotation>();
        foreach (var ta in textMarkupAnnotations)
        {
            Console.WriteLine($"[{ta.AnnotationType} {ta.Rect}]");
        }
    }
}

Delete Text Markup Annotation

The following code snippet shows how to Delete Text Markup Annotation from PDF file.

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void DeleteTextMarkupAnnotation()
{
    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "sample_mod.pdf"))
    {
        var textMarkupAnnotations = document.Pages[1].Annotations
            .Where(a => a.AnnotationType == Aspose.Pdf.Annotations.AnnotationType.Highlight
            ||a.AnnotationType == Aspose.Pdf.Annotations.AnnotationType.Squiggly)
            .Cast<Aspose.Pdf.Annotations.TextMarkupAnnotation>();
        foreach (var ta in textMarkupAnnotations)
        {
            document.Pages[1].Annotations.Delete(ta);
        }
        
        // Save PDF document
        document.Save(dataDir + "DeleteTextMarkupAnnotation_out.pdf");
    }
}
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