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C#/VB.NET: Add Text Watermarks to PDF

2021-12-14 09:14:00 Written by  support iceblue
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To prevent your PDF document from being used in an unauthorized manner, you can watermark the document with text or an image. In this article, you will learn how to programmatically add text watermarks (single-line and multi-line watermarks) to PDF in C# and VB.NET using Spire.PDF for .NET.

Install Spire.PDF for .NET

To begin with, you need to add the DLL files included in the Spire.PDF for.NET package as references in your .NET project. The DLLs files can be either downloaded from this link or installed via NuGet.

  • Package Manager
PM> Install-Package Spire.PDF 

Add a Text Watermark to PDF

Spire.PDF does not provide an interface or a class to deal with watermarks in PDF files. You could, however, draw text like "confidential", "internal use", or "draft" on each page to mimic the watermark effect. The following are the main steps to add a text watermark to all pages of a PDF document.

  • Create a PdfDocument object and load a sample PDF document using PdfDocument.LoadFromFile() method.
  • Create a PdfTrueTypeFont object, specify the watermark text, and measure the text size using PdfFontBase.MeasureString() method.
  • Traverse all the pages in the document.
  • Translate the coordinate system of a certain page by specified coordinates using PdfPageBase.Canvas.TraslateTransform() method, and rotate the coordinate system 45 degrees counterclockwise using PdfPageBase.Canvas.RotateTransform() method. This ensures that the watermark will appear in the middle of the page at a 45-degree angle.
  • Draw the watermark text on the page using PdfPageBase.Canvas.DrawString() method.
  • Save the document to a different PDF file using PdfDocument.SaveToFile() method.
  • C#
  • VB.NET
using Spire.Pdf;
using Spire.Pdf.Graphics;
using System.Drawing;

namespace AddTextWatermarkToPdf
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument pdf = new PdfDocument();

            //Load a sample PDF document
            pdf.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");

            //Create a PdfTrueTypeFont object
            PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", 50f), true);

            //Set the watermark text
            string text = "CONFIDENTIAL";

            //Measure the text size
            SizeF textSize = font.MeasureString(text);

            //Calculate the values of two offset variables, 
            //which will be used to calculate the translation amount of the coordinate system
            float offset1 = (float)(textSize.Width * System.Math.Sqrt(2) / 4);
            float offset2 = (float)(textSize.Height * System.Math.Sqrt(2) / 4);

            //Traverse all the pages in the document
            foreach (PdfPageBase page in pdf.Pages)
            {
                //Set the page transparency
                page.Canvas.SetTransparency(0.8f);

                //Translate the coordinate system by specified coordinates
                page.Canvas.TranslateTransform(page.Canvas.Size.Width / 2 - offset1 - offset2, page.Canvas.Size.Height / 2 + offset1 - offset2);

                //Rotate the coordinate system 45 degrees counterclockwise
                page.Canvas.RotateTransform(-45);

                //Draw watermark text on the page
                page.Canvas.DrawString(text, font, PdfBrushes.DarkGray, 0, 0);
            }

            //Save the changes to another file
            pdf.SaveToFile("TextWatermark.pdf");
        }
    }
}
Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports System.Drawing
 
Namespace AddTextWatermarkToPdf
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a PdfDocument object
            Dim pdf As PdfDocument =  New PdfDocument() 
 
            'Load a sample PDF document
            pdf.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
 
            'Create a PdfTrueTypeFont object
            Dim font As PdfTrueTypeFont =  New PdfTrueTypeFont(New Font("Arial",50f),True) 
 
            'Set the watermark text
            Dim text As String =  "CONFIDENTIAL" 
 
            'Measure the text size
            Dim textSize As SizeF =  font.MeasureString(text) 
 
            'Calculate the values of two offset variables, 
            'which will be used to calculate the translation amount of the coordinate system
            Dim offset1 As single = CType((textSize.Width * System.Math.Sqrt(2) / 4), single)
            Dim offset2 As single = CType((textSize.Height * System.Math.Sqrt(2) / 4), single)
 
            'Traverse all the pages in the document
            Dim page As PdfPageBase
            For Each page In pdf.Pages
                'Set the page transparency
                page.Canvas.SetTransparency(0.8f)
 
                'Translate the coordinate system by specified coordinates
                page.Canvas.TranslateTransform(page.Canvas.Size.Width / 2 - offset1 - offset2, page.Canvas.Size.Height / 2 + offset1 - offset2)
 
                'Rotate the coordinate system 45 degrees counterclockwise
                page.Canvas.RotateTransform(-45)
 
                'Draw watermark text on the page
                page.Canvas.DrawString(text, font, PdfBrushes.DarkGray, 0, 0)
            Next
 
            'Save the changes to another file
            pdf.SaveToFile("TextWatermark.pdf")
        End Sub
    End Class
End Namespace

C#/VB.NET: Add Text Watermarks to PDF

Add Multi-Line Text Watermarks to PDF

There are times when you may want to add more than one line of text watermarks to your document. To achieve the tiled watermark effect, you can make use of PdfTilingBrush class, which produces a tiled pattern that is repeated to fill a graphics area. The following are the main steps to add multi-line watermarks to a PDF document.

  • Create a PdfDocument object and load a sample PDF document using PdfDocument.LoadFromFile() method.
  • Create a custom method InsertMultiLineTextWatermark(PdfPageBase page, String watermarkText, PdfTrueTypeFont font, int rowNum, int columnNum) to add multi-line text watermarks to a PDF page. The parameters rowNum and columnNum specify the row and column number of the tiled watermarks.
  • Traverse all pages in the document, and call the custom method InsertMultiLineTextWatermark() to apply watermarks to each page.
  • Save the document to another file using PdfDocument.SaveToFile() method.
  • C#
  • VB.NET
using System;
using Spire.Pdf;
using Spire.Pdf.Graphics;
using System.Drawing;

namespace AddMultiLineTextWatermark
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument instance
            PdfDocument pdf = new PdfDocument();

            //Load a sample PDF document
            pdf.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.pdf");

            //Create a PdfTrueTypeFont object
            PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", 20f), true);

            //Traverse all the pages
            for (int i = 0; i < pdf.Pages.Count; i++)
            {
                //Call InsertMultiLineTextWatermark() method to add text watermarks to the specified page
                InsertMultiLineTextWatermark(pdf.Pages[i], "E-ICEBLUE CO LTD", font, 3, 3);
            }

            //Save the document to another file
            pdf.SaveToFile("MultiLineTextWatermark.pdf");
        }

        //Create a custom method to insert multi-line text watermarks to a page
        static void InsertMultiLineTextWatermark(PdfPageBase page, String watermarkText, PdfTrueTypeFont font, int rowNum, int columnNum)
        {
            //Measure the text size
            SizeF textSize = font.MeasureString(watermarkText);

            //Calculate the values of two offset variables, which will be used to calculate the translation amount of coordinate system
            float offset1 = (float)(textSize.Width * System.Math.Sqrt(2) / 4);
            float offset2 = (float)(textSize.Height * System.Math.Sqrt(2) / 4);

            //Create a tile brush
            PdfTilingBrush brush = new PdfTilingBrush(new SizeF(page.ActualSize.Width / columnNum, page.ActualSize.Height / rowNum));
            brush.Graphics.SetTransparency(0.3f);
            brush.Graphics.Save();
            brush.Graphics.TranslateTransform(brush.Size.Width / 2 - offset1 - offset2, brush.Size.Height / 2 + offset1 - offset2);
            brush.Graphics.RotateTransform(-45);

            //Draw watermark text on the tile brush
            brush.Graphics.DrawString(watermarkText, font, PdfBrushes.Violet, 0, 0);
            brush.Graphics.Restore();

            //Draw a rectangle (that covers the whole page) using the tile brush
            page.Canvas.DrawRectangle(brush, new RectangleF(new PointF(0, 0), page.ActualSize));
        }
    }
}
Imports System
Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports System.Drawing
 
Namespace AddMultiLineTextWatermark
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a PdfDocument instance
            Dim pdf As PdfDocument =  New PdfDocument() 
 
            'Load a sample PDF document
            pdf.LoadFromFile("C:\Users\Administrator\Desktop\sample.pdf")
 
            'Create a PdfTrueTypeFont object
            Dim font As PdfTrueTypeFont =  New PdfTrueTypeFont(New Font("Arial",20f),True) 
 
            'Traverse all the pages
            Dim i As Integer
            For  i = 0 To  pdf.Pages.Count- 1  Step  i + 1
                'Call InsertMultiLineTextWatermark() method to add text watermarks to the specified page
                InsertMultiLineTextWatermark(pdf.Pages(i), "E-ICEBLUE CO LTD", font, 3, 3)
            Next
 
            'Save the document to another file
            pdf.SaveToFile("MultiLineTextWatermark.pdf")
        End Sub
 
        'Create a custom method to insert multi-line text watermarks to a page
        Shared  Sub InsertMultiLineTextWatermark(ByVal page As PdfPageBase, ByVal watermarkText As String, ByVal font As PdfTrueTypeFont, ByVal rowNum As Integer, ByVal columnNum As Integer)
            'Measure the text size
            Dim textSize As SizeF =  font.MeasureString(watermarkText) 
 
            'Calculate the values of two offset variables, which will be used to calculate the translation amount of coordinate system
            Dim offset1 As single = CType((textSize.Width * System.Math.Sqrt(2) / 4), single)
            Dim offset2 As single = CType((textSize.Height * System.Math.Sqrt(2) / 4), single)
 
            'Create a tile brush
            Dim brush As PdfTilingBrush =  New PdfTilingBrush(New SizeF(page.ActualSize.Width / columnNum,page.ActualSize.Height / rowNum)) 
            brush.Graphics.SetTransparency(0.3f)
            brush.Graphics.Save()
            brush.Graphics.TranslateTransform(brush.Size.Width / 2 - offset1 - offset2, brush.Size.Height / 2 + offset1 - offset2)
            brush.Graphics.RotateTransform(-45)
 
            'Draw watermark text on the tile brush
            brush.Graphics.DrawString(watermarkText, font, PdfBrushes.Violet, 0, 0)
            brush.Graphics.Restore()
 
            'Draw a rectangle (that covers the whole page) using the tile brush
            page.Canvas.DrawRectangle(brush, New RectangleF(New PointF(0, 0), page.ActualSize))
        End Sub
    End Class
End Namespace

C#/VB.NET: Add Text Watermarks to PDF

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Last modified on Tuesday, 20 June 2023 02:04