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C# PDF Annotation Library
How to search, highlight specific PDF text programmatically using C#.NET


Sample Codes for C#.NET Users to Highlight Selected PDF Text on PDF Page in C#.NET Class. Free Download. ASP.NET Annotate PDF function is based on C# PDF Annotate SDK.





In this tutorial, you will learn how to add, insert, extract, read, remove "Highlight Text" comments to pdf file in C#.

  • Add, insert new highlight text annotations to PDF file
  • Customize the text highlight annotation with color and transparency options
  • Read existing text highlight annotation's data
  • Remove text annotations

How to add, remove Highlight Text comments to existing PDF file using C#

  1. Download XDoc.PDF Text Annotation C# library
  2. Install C# library to edit Text comment to PDF document
  3. Step by Step Tutorial








  • Best PDF document reader SDK control that can highlight PDF text in Visual C# .NET framework application
  • A professional annotation application able to highlight PDF file in C#.NET WinForm project without adobe reader components
  • Support .NET WinForms, ASP.NET MVC in IIS, ASP.NET Ajax, Azure cloud service, DNN (DotNetNuke), SharePoint
  • An ASP.NET web-server compliant library able to highlight text in PDF file online in browser such as chrome, firefox, safari, etc
  • Able to remove highlighted text in PDF document in C#.NET
  • Support to change PDF highlight color in Visual C# .NET class
  • Able to save highlighted content to original PDF document
  • Various C# source codes provides multiple ways to highlight PDF text in .NET


Users will often face the situation that you may need to emphasize the most important information from all text on a PDF page. Highlight text is such a functionality which allow users to give prominence to key words or sentences. RasterEdge XDoc.PDF SDK is a multifunctional PDF document annotation tool, which can highlight text with a simple piece of C# programming demo code.

Since RasterEdge XDoc.PDF SDK is based on .NET framework 2.0, users are enabled to use it in any type of a 32-bit or 64-bit .NET application, including ASP.NET web service and Windows Forms for any .NET Framework version from 2.0 to 4.5.





C# add highlight text annotation to pdf document



You can add, insert a highlight text comment using class PDFAnnotHighlight using C#. When adding a new highlight text comment, you need specify a rectangle area which the highlight text commend will cover.

The C# source code below will show how to add text highlight annotation on specific text in PDF page.

  • Create a PDFDocument object from an existing PDF file
  • Get the second page of the PDF document
  • Create a PDFAnnotHighlight object with StartPoint, and EndPoint property value set
  • Utilize PDFPage.AddPDFAnnot() to add the text highlight annotation object to PDF page
  • Save the modified PDF file with text highlight annotation created



String inputFilePath = Program.RootPath + "\\" + "2.pdf";
String outputFilePath = Program.RootPath + "\\" + "Annot_3.pdf";

//  open a PDF file
PDFDocument doc = new PDFDocument(inputFilePath);
//  get the 2nd page
PDFPage page = (PDFPage)doc.GetPage(1);

//  create the annotation
PDFAnnotHighlight annot = new PDFAnnotHighlight();

annot.StartPoint = new PointF(100F, 200F);
annot.EndPoint = new PointF(300F, 400F);

//  add annotation to the page
page.AddPDFAnnot(annot);

//  save to a new file
doc.Save(outputFilePath);




C# read highlight text annotation from pdf document


The following C# code shows how to read text comment information. Each highlight text annotation will include: highlight fill color, and covered area on the page.



String inputFilePath = Program.RootPath + "\\" + "Annot_3.pdf";

PDFDocument doc = new PDFDocument(inputFilePath);
List<IPDFAnnot> annots = PDFAnnotHandler.GetAllAnnotations(doc);
foreach (IPDFAnnot annot in annots)
{
    if (annot is PDFAnnotHighlight)
    {
        PDFAnnotHighlight obj = (PDFAnnotHighlight)annot;
        Console.WriteLine("Color: " + obj.Color.ToString());
        Console.WriteLine("Line Boundaries: ");
        foreach (RectangleF line in obj.GetLineBoundaries())
        {
            Console.WriteLine("  " + line.ToString());
        }
    }
}




C# delete all annotations from pdf document


String inputFilePath = Program.RootPath + "\\" + "1_Annots.pdf";

PDFDocument doc = new PDFDocument(inputFilePath);
//  get all annotations in the 1st page
PDFPage page = (PDFPage)doc.GetPage(0);
List<IPDFAnnot> annots = PDFAnnotHandler.GetAllAnnotations(page);
//  remove all annotations in the 1st page
PDFAnnotHandler.DeleteAnnotation(doc, annots);