How to add watermark to PDF file in C#, VB.NET?
Watermark is a text, image, logo, or a graphical shape that appears in front of an existing PDF document. For example, you can apply a “Confidential” text to the pages with sensitive information.
Syncfusion Essential PDF is a .NET PDF library used to create, read, and edit PDF documents. Using this library, you can add watermark to PDF file in C# and VB.
Steps to create a PDF programmatically:
- Create a new C# console application project.
- Install the Syncfusion.Pdf.WinForms NuGet package as reference to your .NET Framework application from NuGet.org.
- Include the following namespace in the Program.cs file.
C#
using Syncfusion.Pdf;
using Syncfusion.Pdf.Graphics;
using Syncfusion.Pdf.Parsing;
using System.Drawing;
VB.NET
Imports Syncfusion.Pdf
Imports Syncfusion.Pdf.Graphics
Imports Syncfusion.Pdf.Parsing
Imports System.Drawing
- Use the following code snippet to add watermark to an existing PDF.
C#
//Load the document
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");
//Get first page from document
PdfPageBase loadedPage = loadedDocument.Pages[0];
//Create PDF graphics for the page
PdfGraphics graphics = loadedPage.Graphics;
//Set font for the watermark text
PdfFont font = new PdfStandardFont(PdfFontFamily.Helvetica, 20);
//Save the graphics state for the watermark text
PdfGraphicsState state = graphics.Save();
//Set transparency level for the text
graphics.SetTransparency(0.25f);
//Rotate the text to -40 Degree
graphics.RotateTransform(-40);
//Draw the watermark text to the desired position over the PDF page with red color
graphics.DrawString("Confidential", font, PdfPens.Red, PdfBrushes.Red, new PointF(0, 250));
//Save the document
loadedDocument.Save("watermark.pdf");
//Close the document
loadedDocument.Close(true);
Process.Start("watermark.pdf");
VB.NET
'Load the document
Dim loadedDocument As New PdfLoadedDocument("Input.pdf")
'Get first page from document
Dim loadedPage As PdfPageBase = loadedDocument.Pages(0)
'Create PDF graphics for the page
Dim graphics As PdfGraphics = loadedPage.Graphics
'Set font for the watermark text
Dim font As PdfFont = New PdfStandardFont(PdfFontFamily.Helvetica, 20)
' Save the graphics state for the watermark text
Dim state As PdfGraphicsState = graphics.Save()
' Set transparency level for the text
graphics.SetTransparency(0.25F)
' Rotate the text to -40 Degree
graphics.RotateTransform(-40)
' Draw the watermark text to the desired position over the PDF page with red color
graphics.DrawString("Confidential", font, PdfPens.Red, PdfBrushes.Red, New PointF(0, 250))
'Save the document
loadedDocument.Save("watermark.pdf")
'Close the document
loadedDocument.Close(True)
Process.Start("watermark.pdf")
You can download the working sample from CreateWatermarkPDFSample.Zip
By executing the program, you will get the PDF document as follows. 
Take a moment to peruse the documentation, where you can find other options like adding image watermark in PDF document and features like images to PDF, Text to PDF, Layers, etc., with code examples.
Refer here to explore the rich set of Syncfusion Essential PDF features.
An online sample link to generate watermark 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.
