How to: Highlight Search Results in a PDF File

• Sep 19, 2023
• 3 minutes to read

This example shows how to highlight search results in a document. You can use PDF Graphics to draw filled rectangles around text or add annotations to highlight search results.

Use PDF Graphics

Create a RectangleF object around the search result. Use the PdfGraphics.FillRectangle method to draw a rectangle around search text. The PdfGraphics.AddToPageForeground method allows you apply filled rectangles to the page.

C#

static void HighlightResultWithGraphics(PdfDocumentProcessor processor, PdfTextSearchResults result)
{
    using (PdfGraphics graphics = processor.CreateGraphics()) 
    {
        for (int i = 0; i < result.Rectangles.Count; i++)
        {
            RectangleF rect = new RectangleF(new PointF((float)result.Rectangles[i].Left, (float)result.Page.CropBox.Height - (float)result.Rectangles[i].Top),
                new SizeF((float)result.Rectangles[i].Width, (float)result.Rectangles[i].Height));
            using (var brush = new SolidBrush(Color.FromArgb(130, 55, 155, 255)))
                graphics.FillRectangle(brush, rect);
        }
        graphics.AddToPageForeground(result.Page, 72, 72);
    }
}

VB.NET

Private Shared Sub HighlightResultWithGraphics(ByVal processor As PdfDocumentProcessor, ByVal result As PdfTextSearchResults)
    Using graphics As PdfGraphics = processor.CreateGraphics()
        For i As Integer = 0 To result.Rectangles.Count - 1
            Dim rect As RectangleF = New RectangleF(New PointF(CSng(result.Rectangles(i).Left), CSng(result.Page.CropBox.Height) - CSng(result.Rectangles(i).Top)), New SizeF(CSng(result.Rectangles(i).Width), CSng(result.Rectangles(i).Height)))
            Using brush = New SolidBrush(Color.FromArgb(130, 55, 155, 255))
                graphics.FillRectangle(brush, rect)
            End Using
        Next

Use Annotations

Call the PdfDocumentProcessor.AddTextMarkupAnnotation method to add an annotation to the search results. Use the PdfTextSearchResults.Rectangles property to access the document areas that contain search text. The PdfAnnotationData.Color property specifies the annotation color.

C#

static void HighlightResultUsingAnnotations(PdfDocumentProcessor processor, PdfTextSearchResults result)
{
    for (int i = 0; i < result.Rectangles.Count; i++)
    {
        PdfTextMarkupAnnotationData annotation =
        processor.AddTextMarkupAnnotation(result.PageNumber, result.Rectangles[i], PdfTextMarkupAnnotationType.Highlight);
        if (annotation != null)
        {
            annotation.Color = new PdfRGBColor(0.2, 0.6, 0);
        }
    }
}

VB.NET

Private Shared Sub HighlightResultUsingAnnotations(ByVal processor As PdfDocumentProcessor, ByVal result As PdfTextSearchResults)
    For i As Integer = 0 To result.Rectangles.Count - 1
        Dim annotation As PdfTextMarkupAnnotationData = processor.AddTextMarkupAnnotation(result.PageNumber, result.Rectangles(i), PdfTextMarkupAnnotationType.Highlight)
        If annotation IsNot Nothing Then
            annotation.Color = New PdfRGBColor(0.2, 0.6, 0)
        End If
    Next
End Sub

Search and Highlight Text

The code example below shows how to use the PdfDocumentProcessor.FindText method to search text. (If you wish to highlight the results, you can also use the HighlightResult method - as described above.)

View Example

Program.cs

using (PdfDocumentProcessor documentProcessor = new PdfDocumentProcessor())
{
    //Define search words
    string[] words = { "Get", "DX-RX809", "HD", "DX-B5000" };

    //Load a PDF document
    documentProcessor.LoadDocument(@"..\..\Document.pdf");

    //Specify the search parameters
    PdfTextSearchParameters searchParameters = new PdfTextSearchParameters();
    searchParameters.CaseSensitive = true;
    searchParameters.WholeWords = true;

    foreach (string word in words) 
    {
        PdfTextSearchResults result;
        //Get the search results from the FindText method call with search text and search parameters
        while ((result = documentProcessor.FindText(word, searchParameters)).Status == PdfTextSearchStatus.Found) 
        {
            //HighlightResultWithGraphics(documentProcessor, result);
            HighlightResultUsingAnnotations(documentProcessor, result);
        }
    }
    //Save the document
    documentProcessor.SaveDocument(@"..\..\Result.pdf");
}

Program.vb

Using documentProcessor As PdfDocumentProcessor = New PdfDocumentProcessor()
    'Define search words
    Dim words As String() = {"Get", "DX-RX809", "HD", "DX-B5000"}
    'Load a PDF document
    documentProcessor.LoadDocument("..\..\Document.pdf")
    'Specify the search parameters
    Dim searchParameters As PdfTextSearchParameters = New PdfTextSearchParameters()
    searchParameters.CaseSensitive = True
    searchParameters.WholeWords = True
    For Each word As String In words
        Dim result As PdfTextSearchResults
        'Get the search results from the FindText method call with search text and search parameters
        While(CSharpImpl.__Assign(result, documentProcessor.FindText(word, searchParameters))).Status = PdfTextSearchStatus.Found
            'HighlightResultWithGraphics(documentProcessor, result);
            HighlightResultUsingAnnotations(documentProcessor, result)
        End While
    Next

    'Save the document
    documentProcessor.SaveDocument("..\..\Result.pdf")
End Using