c# itextsharp PDF creation with watermark on each page

Question

I am trying to programmatically create a number of PDF documents with a watermark on each page using itextsharp (a C# port of Java's itext).

I am able to do this after the document has been created using a PdfStamper. However this seems to involve re-opening the document reading it and then creating a new document with the watermark on each page.

Is there a way of doing this during document creation?

Answer 1

After digging into it I found the best way was to add the watermark to each page as it was created. To do this I created a new class and implemented the IPdfPageEvent interface as follows:

    class PdfWriterEvents : IPdfPageEvent
    {
        string watermarkText = string.Empty;

        public PdfWriterEvents(string watermark) 
        {
            watermarkText = watermark;
        }

        public void OnOpenDocument(PdfWriter writer, Document document) { }
        public void OnCloseDocument(PdfWriter writer, Document document) { }
        public void OnStartPage(PdfWriter writer, Document document) {
            float fontSize = 80;
            float xPosition = 300;
            float yPosition = 400;
            float angle = 45;
            try
            {
                PdfContentByte under = writer.DirectContentUnder;
                BaseFont baseFont = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.WINANSI, BaseFont.EMBEDDED);
                under.BeginText();
                under.SetColorFill(BaseColor.LIGHT_GRAY);
                under.SetFontAndSize(baseFont, fontSize);
                under.ShowTextAligned(PdfContentByte.ALIGN_CENTER, watermarkText, xPosition, yPosition, angle);
                under.EndText();
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine(ex.Message);
            }
        }
        public void OnEndPage(PdfWriter writer, Document document) { }
        public void OnParagraph(PdfWriter writer, Document document, float paragraphPosition) { }
        public void OnParagraphEnd(PdfWriter writer, Document document, float paragraphPosition) { }
        public void OnChapter(PdfWriter writer, Document document, float paragraphPosition, Paragraph title) { }
        public void OnChapterEnd(PdfWriter writer, Document document, float paragraphPosition) { }
        public void OnSection(PdfWriter writer, Document document, float paragraphPosition, int depth, Paragraph title) { }
        public void OnSectionEnd(PdfWriter writer, Document document, float paragraphPosition) { }
        public void OnGenericTag(PdfWriter writer, Document document, Rectangle rect, String text) { }

    }
}

This object is registered to handle the events as follows:

PdfWriter docWriter = PdfWriter.GetInstance(document, new FileStream(outputLocation, FileMode.Create));
PdfWriterEvents writerEvent = new PdfWriterEvents(watermark);
docWriter.PageEvent = writerEvent;