How to: Add Watermark to PDFs Programmatically using iTextSharp

Being able to add text or image watermark to PDF files is one of those handy things you can archive via program.

The only library required for the little program is iTextSharp. For those who haven't used it yet, iTextSharp is a C# version of iText, which allows you to generate or manipulate PDFs.

So let's cut the chitchat, and go straight to the code. By calling 'AddTextWatermark' or 'AddImageWatermark' function with required parameters supplied, you are ready to rock!

public void CreateTemplate(string watermarkText, string targetFileName){
    var document = new Document();
    var pdfWriter = PdfWriter.GetInstance(document, new FileStream(targetFileName, FileMode.Create));
    var font = new Font(Font.FontFamily.HELVETICA, 60, Font.NORMAL, BaseColor.LIGHT_GRAY);
    document.Open();
    // Specify font and alignment of text watermark
    ColumnText.ShowTextAligned(pdfWriter.DirectContent, Element.ALIGN_CENTER, new Phrase(watermarkText, font), 300, 400, 45);
    document.Close();
}

// Add watermark using a PDF file
public void AddTextWatermark(string sourceFilePath, string watermarkTemplatePath, string targetFilePath){
    var pdfReaderSource = new PdfReader(sourceFilePath);
    var pdfStamper = new PdfStamper(pdfReaderSource, new FileStream(targetFilePath, FileMode.Create));
    var pdfReaderTemplate = new PdfReader(watermarkTemplatePath);
    var page = pdfStamper.GetImportedPage(pdfReaderTemplate, 1);

    for (var i = 0; i < pdfReaderSource.NumberOfPages; i++)
    {
        var content = pdfStamper.GetUnderContent(i + 1);
        content.AddTemplate(page, 0, 0);
    }

    pdfStamper.Close();
    pdfReaderTemplate.Close();
}

// Add watermark to a file using an image
public void AddImageWatermark(string sourceFilePath, string watermarkImagePath, string targetFilePath){
    var pdfReader = new PdfReader(sourceFilePath);
    var pdfStamper = new PdfStamper(pdfReader, new FileStream(targetFilePath, FileMode.Create));
    var image = Image.GetInstance(watermarkImagePath);
    image.SetAbsolutePosition(200, 400);

    for (var i = 0; i < pdfReader.NumberOfPages; i++)
    {
        var content = pdfStamper.GetUnderContent(i + 1);
        content.AddImage(image);
    }

    pdfStamper.Close();
}