Add Watermark to PDF document in ASP.NET using iTextsharp dll file

The following code will add watermark text to pdf document

You need to add the following headers to your aspx page

using iTextSharp;
using iTextSharp.text;
using iTextSharp.text.pdf;


The following method will add watermark text

public  static byte[] WriteToPdf(FileInfo sourceFile, string stringToWriteToPdf)
{
PdfReader reader = new PdfReader(sourceFile.FullName);
using (MemoryStream memoryStream = new MemoryStream())
{
PdfStamper pdfStamper = new PdfStamper(reader, memoryStream);
for (int i = 1; i <= reader.NumberOfPages; i++)
{
Rectangle pageSize = reader.GetPageSizeWithRotation(i);
PdfContentByte pdfPageContents = pdfStamper.GetUnderContent(i);
pdfPageContents.BeginText();
BaseFont baseFont = BaseFont.CreateFont(BaseFont.HELVETICA_BOLD, BaseFont.CP1252, false);
pdfPageContents.SetFontAndSize(baseFont,80);
pdfPageContents.SetRGBColorFill(137, 142, 136);
float textAngle =(float) GetHypotenuseAngleInDegreesFrom(pageSize.Height, pageSize.Width);
pdfPageContents.ShowTextAligned(PdfContentByte.ALIGN_CENTER, stringToWriteToPdf, pageSize.Width/2, pageSize.Height/2, textAngle);
pdfPageContents.EndText();
}
pdfStamper.FormFlattening = true;
pdfStamper.Close();
reader.Close();
return memoryStream.ToArray();
}
}
The following method will set the angle for the watermark text

public static double GetHypotenuseAngleInDegreesFrom(double opposite, double adjacent)
{
double radians = Math.Atan2(opposite, adjacent);
double angle = radians*(180/Math.PI);
return angle;
}


Output :