How to use a large image in header?

//Creates a new Pdf Document
PdfDocument document = new PdfDocument();
//Sets the font
PdfFont font = new PdfStandardFont(PdfFontFamily.Helvetica, 20f);
//Creates brush
PdfBrush brush = PdfBrushes.Black;
//Create PdfPageTemplateElement by setting width and height
PdfPageTemplateElement template = new PdfPageTemplateElement(510, 100);
PdfBitmap image = new PdfBitmap(filePath);
//Draw image from the page template graphics
template.Graphics.DrawImage(image, 0, 0, template.Width, template.Height);
//Draw string from the page template graphics
template.Graphics.DrawString("Welcome to First Page", font, brush, 40, 50);
//Set image drawn template to document template's top position which makes image to appear in header
document.Template.Top = template;
//Adds page
PdfPage page = document.Pages.Add();
//Save the document and dispose it
document.Save("sample.pdf", Response, HttpReadType.Save);
document.Close();