How to add a watermark in the center of the page in a PDF document using C# and VB.NET

using Syncfusion.Pdf;
using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Graphics;
using System.Drawing;

Imports Syncfusion.Pdf
Imports Syncfusion.Pdf.Parsing
Imports Syncfusion.Pdf.Graphics
Imports System.Drawing

//Load an existing PDF document 
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("../../Data/Barcode.pdf");
 
//Set the font
PdfFont font = new PdfStandardFont(PdfFontFamily.Helvetica, 20);
 
string watermarkText = "Imported using Essential PDF";
 
//Calculate the watermark text size
SizeF size = font.MeasureString(watermarkText);
 
for (int i=0;i<loadedDocument.Pages.Count;i++)
{
    //Load PDF pages
    PdfLoadedPage loadedPage = loadedDocument.Pages[i] as PdfLoadedPage;
 
    //Create graphics for the existing page
    PdfGraphics graphics = loadedPage.Graphics;
 
    float x = loadedPage.Size.Width / 2 - size.Width / 2;
    float y = loadedPage.Size.Height / 2;
 
    //Insert watermark text to PDF 
    PdfGraphicsState state = graphics.Save();
    graphics.SetTransparency(0.25f);
    graphics.DrawString(watermarkText, font, PdfBrushes.Red, new RectangleF(x, y, size.Width, size.Height));
    graphics.Restore();
 
    //Draw string 
    graphics.DrawString("Hello World!!!", font, PdfBrushes.Black, new PointF(0, 0));
}
 
//Save and close the document
loadedDocument.Save("Watermark.pdf");
loadedDocument.Close(true);
 
//This will open the PDF file and the result will be seen in the default PDF Viewer
Process.Start("Watermark.pdf");

'Load an existing PDF document  
Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument("../../Data/Barcode.pdf")
 
'Set the font 
Dim font As PdfFont = New PdfStandardFont(PdfFontFamily.Helvetica, 20)
 
Dim watermarkText As String = "Imported using Essential PDF"
 
'Calculate the watermark text size 
Dim size As SizeF = font.MeasureString(watermarkText)
 
For i As Integer = 0 To loadedDocument.Pages.Count - 1
 
    'Load PDF pages 
    Dim loadedPage As PdfLoadedPage = TryCast(loadedDocument.Pages(i), PdfLoadedPage)
 
    'Create graphics for the existing page 
    Dim graphics As PdfGraphics = loadedPage.Graphics
 
    Dim x As Single = loadedPage.Size.Width / 2 - size.Width / 2
    Dim y As Single = loadedPage.Size.Height / 2
 
    'Insert watermark text to PDF  
    Dim state As PdfGraphicsState = graphics.Save()
    graphics.SetTransparency(0.25F)
    graphics.DrawString(watermarkText, font, PdfBrushes.Red, New RectangleF(x, y, size.Width, size.Height))
    graphics.Restore()
 
    'Draw string  
    graphics.DrawString("Hello World!!!", font, PdfBrushes.Black, New PointF(0, 0))
 
Next
 
'Save and close the document 
loadedDocument.Save("Watermark.pdf")
loadedDocument.Close(True)
 
'This will open the PDF file and the result will be seen in the default PDF Viewer
Process.Start("Watermark.pdf")