How to include rotated watermarks in center of the page in PDF document

// Create a new instance of PdfDocument class.
PdfDocument document = new PdfDocument();
// Add a page to the document.
PdfPage page = document.Pages.Add();
// Create Pdf graphics for the page.
PdfGraphics graphics = page.Graphics;
//Create a font
PdfFont font = new PdfTrueTypeFont(new System.Drawing.Font("Arial", 20,FontStyle.Bold), true);
//save the grapics state
PdfGraphicsState state = graphics.Save();
//Translate the page graphics to be in center.
graphics.TranslateTransform(page.GetClientSize().Width / 2, page.GetClientSize().Height / 2);
//Set the transparency
graphics.SetTransparency(0.20f);
//Set the rotation
graphics.RotateTransform(-20);
string watermarkText = "Imported Using Essential PDF";
// Measure the size of the watermark text
SizeF waterMarkSize= font.MeasureString(watermarkText);
//Draw the watermark text.
graphics.DrawString(watermarkText, font, PdfPens.Red, new PointF(-waterMarkSize.Width/2, -waterMarkSize.Height/2));
//Restore the graphics
graphics.Restore();
// Save the document and dispose it.
document.Save("Sample.pdf");
document.Close(true);