How to: Highlight Search Results in a PDF File

• Apr 28, 2025
• 4 minutes to read

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

Convert Page Coordinates to World Coordinates

Simple

The PdfDocumentProcessor.FindText method returns the search results in the page coordinates. To draw filled rectangles that correspond to the document area containing found text, you need to convert page coordinates to world coordinates since the PdfGraphics.FillRectangle method uses world coordinates.

Use the following formula to convert the page coordinates (points) to world coordinates (units):

unitX = (x / 72) * dpiX;

unitY = ((cropBox.Height -  y) / 72) * dpiY

In this example, the conversion is made in the following method. Please note that the used PdfGraphics.AddToPageForeground method overload allows you to specify dpiX and dpiY values as parameters. The method converts the given (72) DPI value to its native DPI (96) internally.

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 DXSolidBrush(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 DXSolidBrush(Color.FromArgb(130, 55, 155, 255))
                graphics.FillRectangle(brush, rect)
            End Using
        graphics.AddToPageForeground(result.Page, 72, 72)
    End Using
End Sub

Custom DPI

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#

}

//This method uses PdfGraphics to highlight text
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 DXSolidBrush(Color.FromArgb(130, 55, 155, 255)))
                graphics.FillRectangle(brush, rect);
        }

VB.NET

    End Using
End Sub

'This method uses PdfGraphics to highlight text
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 New RectangleF(New PointF(CSng(result.Rectangles(i).Left), CSng(result.Page.CropBox.Height - result.Rectangles(i).Top)),

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#

}

//This method uses annotations to highlight text
static void HighlightResultWithAnnotations(PdfDocumentProcessor processor, PdfTextSearchResults result)
{
    PdfDocumentFacade facade = processor.DocumentFacade;
    PdfPageFacade page = facade.Pages[result.Page.GetPageIndex()];

    for (int i = 0; i < result.Rectangles.Count; i++)
    {
        PdfTextMarkupAnnotationFacade annotation =
                  page.AddTextMarkupAnnotation(result.Rectangles[i], PdfTextMarkupAnnotationType.Highlight);

VB.NET

    End Using
End Sub

'This method uses annotations to highlight text
Private Shared Sub HighlightResultWithAnnotations(ByVal processor As PdfDocumentProcessor, ByVal result As PdfTextSearchResults)
    Dim facade As PdfDocumentFacade = processor.DocumentFacade
    Dim page As PdfPageFacade = facade.Pages(result.Page.GetPageIndex())

Search and Highlight Text

The following code sample calls 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

{
    //Create a PDF document processor.
    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);
                HighlightResultWithAnnotations(documentProcessor, result);
            }
        }
        //Save the document

Program.vb

Using documentProcessor As 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 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
        Do While InlineAssignHelper(result, documentProcessor.FindText(word, searchParameters)).Status = PdfTextSearchStatus.Found
            'HighlightResultWithGraphics(documentProcessor, result)
            HighlightResultWithAnnotations(documentProcessor, result)
        Loop
    Next