Watermark Integration in C# and .NET for PDFs

Watermarking is a common method. With the help of the SautinSoft library, you can easily add them to your PDF documents using C# and .NET.

Watermarks serve several purposes:

  • Document protection. Preventing unauthorized use or distribution of confidential documents.
  • Creating a corporate identity. Add company logos or text to preserve the corporate identity.
  • Specify the status. Mark the documents as "Confidential", "Draft" or "Approved".
  • Copyright protection. Protect intellectual property by using visible watermarks.

The process of adding watermarks to an existing file consists of several steps:

  1. Add SautinSoft.PDF from NuGet.
  2. Load a PDF Document.
  3. Download a PDF document.
  4. Upload an image and set a watermark from a file for each page in the document.
  5. Place the watermark in the center of the page.
  6. Scale the watermark to fit the page size.
  7. Draw a watermark.
  8. Save the document.

Input file:

Output result:

Complete code

using System;
using System.IO;
using SautinSoft;
using SautinSoft.Pdf;
using SautinSoft.Pdf.Content;

namespace Sample
{
    class Sample
    {
        /// <summary>
        /// Watermarks.
        /// </summary>
        /// <remarks>
        /// Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/watermarks.php
        /// </remarks>
        static void Main(string[] args)
        {
            // Before starting this example, please get a free 100-day trial key:
            // https://sautinsoft.com/start-for-free/

            // Apply the key here:
            // PdfDocument.SetLicense("...");

            string pdfFile = Path.GetFullPath(@"..\..\..\simple text.pdf");

            using (var document = PdfDocument.Load(pdfFile))
            {
                // Load the watermark from a file.
                var image = PdfImage.Load(@"..\..\..\WatermarkImage.png");

                foreach (var page in document.Pages)
                {
                    // Make sure the watermark is correctly transformed even if
                    // the page has a custom crop box origin, is rotated, or has custom units.
                    var transform = page.Transform;
                    transform.Invert();

                    // Center the watermark on the page.
                    var pageSize = page.Size;
                    transform.Translate((pageSize.Width - 1) / 2, (pageSize.Height - 1) / 2);

                    // Calculate the scaling factor so that the watermark fits the page.
                    var cropBox = page.CropBox;
                    var scale = Math.Min(cropBox.Width, cropBox.Height);

                    // Scale the watermark so that it fits the page.
                    transform.Scale(scale, scale, 0.5, 0.5);

                    // Draw the centered and scaled watermark.
                    page.Content.DrawImage(image, transform);
                }

                document.Save("Watermark Images.pdf");
            }

            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo("Watermark Images.pdf") { UseShellExecute = true });
        }
    }
}

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Option Infer On

Imports System
Imports System.IO
Imports SautinSoft
Imports SautinSoft.Pdf
Imports SautinSoft.Pdf.Content

Namespace Sample
	Friend Class Sample
		''' <summary>
		''' Watermarks.
		''' </summary>
		''' <remarks>
		''' Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/watermarks.php
		''' </remarks>
		Shared Sub Main(ByVal args() As String)
			' Before starting this example, please get a free 100-day trial key:
			' https://sautinsoft.com/start-for-free/

			' Apply the key here:
			' PdfDocument.SetLicense("...");

			Dim pdfFile As String = Path.GetFullPath("..\..\..\simple text.pdf")

			Using document = PdfDocument.Load(pdfFile)
				' Load the watermark from a file.
				Dim image = PdfImage.Load("..\..\..\WatermarkImage.png")

				For Each page In document.Pages
					' Make sure the watermark is correctly transformed even if
					' the page has a custom crop box origin, is rotated, or has custom units.
					Dim transform = page.Transform
					transform.Invert()

					' Center the watermark on the page.
					Dim pageSize = page.Size
					transform.Translate((pageSize.Width - 1) \ 2, (pageSize.Height - 1) \ 2)

					' Calculate the scaling factor so that the watermark fits the page.
					Dim cropBox = page.CropBox
					Dim scale = Math.Min(cropBox.Width, cropBox.Height)

					' Scale the watermark so that it fits the page.
					transform.Scale(scale, scale, 0.5, 0.5)

					' Draw the centered and scaled watermark.
					page.Content.DrawImage(image, transform)
				Next page

				document.Save("Watermark Images.pdf")
			End Using

			System.Diagnostics.Process.Start(New System.Diagnostics.ProcessStartInfo("Watermark Images.pdf") With {.UseShellExecute = True})
		End Sub
	End Class
End Namespace

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