How to Add a Watermark in C# - A Tech Support Guide

Install-Package itext7

using iText.Kernel.Pdf;
using iText.Layout;
using iText.Layout.Element;

// Create a new PDF document
using (PdfDocument document = new PdfDocument(new PdfWriter("output.pdf")))
{
    // Create a new PDF document
    document.AddNewPage();

    // Create a new watermark
    Watermark watermark = new Watermark("Watermark Text", new FontSet());

    // Add the watermark as a header
    document.AddHeaderWatermark(watermark);

    // Add a paragraph to the document
    document.Add(new Paragraph("Document Content"));
}

using iText.Kernel.Pdf;
using iText.Layout;
using iText.Layout.Element;
using iText.Kernel.Pdf.Event;
using iText.Kernel.Geom;

public class WatermarkEvent : PdfPageEventHelper
{
    private Watermark _watermark;

    public WatermarkEvent(Watermark watermark)
    {
        _watermark = watermark;
    }

    public override void OnEndPage(PdfDocument document, PdfPage page)
    {
        base.OnEndPage(document, page);

        // Get the canvas for the current page
        PdfCanvas canvas = new PdfCanvas(page.NewContentStreamBefore(), page.GetResources(), new PdfDocumentPac(document));

        // Calculate the position and size of the watermark
        Rectangle pageSize = page.GetPageSize();
        float x = (pageSize.GetRight() - pageSize.GetLeft()) / 2;
        float y = (pageSize.GetTop() - pageSize.GetBottom()) / 2;
        float width = 200;
        float height = 50;

        // Create a new watermark
        Watermark watermark = new Watermark(_watermark.GetText(), new FontSet());
        watermark.SetFixedSize(width, height);
        watermark.SetHorizontalAlignment(_watermark.GetHorizontalAlignment());
        watermark.SetVerticalAlignment(_watermark.GetVerticalAlignment());

        // Add the watermark to the canvas
        watermark.Draw(canvas, x, y);
    }
}

// Create a new PDF document
using (PdfDocument document = new PdfDocument(new PdfWriter("output.pdf")))
{
    // Create a new watermark
    Watermark watermark = new Watermark("Watermark Text", new FontSet());

    // Add a page event to add the watermark to each page
    document.AddEventHandler(PdfDocumentEvent.END_PAGE, new WatermarkEvent(watermark));

    // Add new pages to the document
    for (int i = 0; i < 5; i++)
    {
        document.AddNewPage();

        // Add a paragraph to the document
        document.Add(new Paragraph("Page " + (i + 1)));
    }
}

In this example, we define a new class called WatermarkEvent, which inherits from PdfPageEventHelper. This class overrides the OnEndPage() method, which is called at the end of each page. We then create a new watermark using the Watermark() constructor, just like in the previous example. However, instead of adding the watermark as a header, we add a page event using the AddEventHandler() method. We then pass an instance of WatermarkEvent that includes the watermark we want to add. Finally, we add five pages to the document, just like in the previous example.

• A watermark is a graphical image or text used to identify the ownership, confidentiality, or origin of a document.
• To add a watermark as a header, you can use the AddHeaderWatermark() method of the PdfDocument class.
• To add a watermark throughout the pages of a PDF document, you can use a PageEvent that overrides the OnEndPage() method.
• The iText 7 library is a powerful PDF manipulation library that supports various features, including watermarking.

References

• iText 7: https://itextpdf.com/itext7
• iText 7 Documentation: https://developers.itextpdf.com/content/itext-7-developer-guide
• GitHub: https://github.com/itext/itext7