How to highlight text in a PDF using C# and VB.NET
Syncfusion Essential PDF is a .NET PDF library used to create, read, and edit PDF documents. Using this library, you can highlight text in PDF document using C# and VB.NET.
Steps to highlight text in PDF programmatically:
- Create a new C# Windows Forms application project.
- Install the Syncfusion.Pdf.WinForms NuGet package as reference to your .NET Framework application from NuGet.org.
- Include the following namespaces in Program.cs file.
C#
using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Interactive; using Syncfusion.Pdf.Parsing; using System.Drawing;
VB.NET
Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Interactive Imports Syncfusion.Pdf.Parsing Imports System.Drawing
- Use the following code snippet to highlight text in PDF document.
C#
//Loads the document
PdfLoadedDocument document = new PdfLoadedDocument("Input.pdf");
//Gets the first page from the document
PdfLoadedPage page = document.Pages[0] as PdfLoadedPage;
//Add a list to maintain extracted text information
List<TextData> extractedText = new List<TextData>();
//Extract text from first page
page.ExtractText(out extractedText);
foreach (TextData textData in extractedText)
{
if (textData.Text == "Hello World")
{
//Add text markup annotation on the bounds of highlighting text
PdfTextMarkupAnnotation textmarkup = new PdfTextMarkupAnnotation(textData.Bounds);
//Sets the markup annotation type as HighLight
textmarkup.TextMarkupAnnotationType = PdfTextMarkupAnnotationType.Highlight;
//Sets the content of the annotation
textmarkup.Text = "Highlight Text";
//Sets the highlighting color
textmarkup.TextMarkupColor = new PdfColor(Color.LightPink);
//Add annotation into page
page.Annotations.Add(textmarkup);
}
}
//Save and close the document
document.Save("HighlightText.pdf");
document.Close(true);
VB.NET
'Loads the document
Dim document As New PdfLoadedDocument("Input.pdf")
'Gets the first page from the document
Dim page As PdfLoadedPage = TryCast(document.Pages(0), PdfLoadedPage)
'Add a list to maintain extracted text information
Dim extractedText As New List(Of TextData)()
'Extract text from first page
page.ExtractText(extractedText)
For Each textData As TextData In extractedText
If textData.Text = "Hello World" Then
'Add text markup annotation on the bounds of highlighting text
Dim textmarkup As New PdfTextMarkupAnnotation(textData.Bounds)
'Sets the markup annotation type as HighLight
textmarkup.TextMarkupAnnotationType = PdfTextMarkupAnnotationType.Highlight
'Sets the content of the annotation
textmarkup.Text = "Highlight Text"
'Sets the highlighting color
textmarkup.TextMarkupColor = New PdfColor(Color.LightPink)
'Add annotation into page
page.Annotations.Add(textmarkup)
End If
Next
'Save and close the document
document.Save("HighlightText.pdf")
document.Close(True)
A complete working sample can be downloaded from HighlightTextInPDF.zip.
By executing the program, you will get the PDF document as follows. 
Take a moment to peruse the documentation for working with annotations, where you can find other options like add, delete, and modify the annotation from the PDF document.
Refer here to explore the rich set of Syncfusion Essential PDF features.
An online sample link to adding various types of annotation to PDF document.
Starting with v16.2.0.x, if you reference Syncfusion assemblies from trial setup or from the NuGet feed, include a license key in your projects. Refer to link to learn about generating and registering Syncfusion license key in your application to use the components without trail message.
