Add Water mark image to PDF using iTextsharp, C# and VB.Net in ASP.Net

Dear sandip.AP,,

please follow below example, it might be helpful

private void PdfStamp(string FileLocation, string sourceFilePath)
        {
            byte[] bytes1 = File.ReadAllBytes(@"Yourpdffilepath");
            
            var img = iTextSharp.text.Image.GetInstance(@"D:/Projects/MaterialDetails/MaterialDetails/img/Stamp.png");
            img.SetAbsolutePosition(200, 400);
            PdfContentByte waterMark;

            using (MemoryStream stream = new MemoryStream())
            {
                PdfReader reader = new PdfReader(bytes1);
                using (PdfStamper stamper = new PdfStamper(reader, stream))
                {
                    int pages = reader.NumberOfPages;
                    for (int i = 1; i <= pages; i++)
                    {
                        // Specify font and alignment of image watermark
                        waterMark = stamper.GetUnderContent(i);
                        waterMark.AddImage(img);
                    }

                }
                bytes1 = stream.ToArray();
            }
            File.WriteAllBytes(@"yourpdffilepath", bytes1);

        }

Hi sandip.AP,

Refer below sample code.

C#

private void PdfStampWithNewFile(string watermarkImagePath, string sourceFilePath, string destinationFilePath)
{
    var pdfReader = new PdfReader(sourceFilePath);
    var pdfStamper = new PdfStamper(pdfReader, new FileStream(destinationFilePath, FileMode.Create));
    var image = iTextSharp.text.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();
}

private void PdfStampInExistingFile(string watermarkImagePath, string sourceFilePath)
{
    byte[] bytes = File.ReadAllBytes(sourceFilePath);
    var img = iTextSharp.text.Image.GetInstance(watermarkImagePath);
    img.SetAbsolutePosition(200, 400);
    PdfContentByte waterMark;

    using (MemoryStream stream = new MemoryStream())
    {
        PdfReader reader = new PdfReader(bytes);
        using (PdfStamper stamper = new PdfStamper(reader, stream))
        {
            int pages = reader.NumberOfPages;
            for (int i = 1; i <= pages; i++)
            {
                waterMark = stamper.GetUnderContent(i);
                waterMark.AddImage(img);
            }
        }
        bytes = stream.ToArray();
    }
    File.WriteAllBytes(sourceFilePath, bytes);
}

VB.Net

Private Sub PdfStampWithNewFile(watermarkImagePath As String, sourceFilePath As String, destinationFilePath As String)
    Dim pdfReader = New iTextSharp.text.pdf.PdfReader(sourceFilePath)
    Dim pdfStamper = New iTextSharp.text.pdf.PdfStamper(pdfReader, New FileStream(destinationFilePath, FileMode.Create))
    Dim image = iTextSharp.text.Image.GetInstance(watermarkImagePath)
    image.SetAbsolutePosition(200, 400)
    For i As Integer = 0 To pdfReader.NumberOfPages - 1
        Dim content = pdfStamper.GetUnderContent(i + 1)
        content.AddImage(image)
    Next
    pdfStamper.Close()
End Sub

Private Sub PdfStampInExistingFile(watermarkImagePath As String, sourceFilePath As String)
    Dim bytes As Byte() = File.ReadAllBytes(sourceFilePath)
    Dim img = iTextSharp.text.Image.GetInstance(watermarkImagePath)
    img.SetAbsolutePosition(200, 400)
    Dim waterMark As PdfContentByte

    Using stream As New MemoryStream()
        Dim reader As New PdfReader(bytes)
        Using stamper As New PdfStamper(reader, stream)
            Dim pages As Integer = reader.NumberOfPages
            For i As Integer = 1 To pages
                waterMark = stamper.GetUnderContent(i)
                waterMark.AddImage(img)
            Next
        End Using
        bytes = stream.ToArray()
    End Using
    File.WriteAllBytes(sourceFilePath, bytes)
End Sub