[.Net C#]利用iTextSharp在PDF上新增浮水印(WaterMark)

public void Watermark(string inputPath, string outputPath, string watermarkPath)
{
try
{
PdfReader reader = new PdfReader(inputPath);
iTextSharp.text.Document document = new iTextSharp.text.Document();
PdfWriter writer = PdfWriter.GetInstance(document,new FileStream(outputPath, FileMode.Create));
Watermark watermark = new Watermark(iTextSharp.text.Image.GetInstance(watermarkPath), 255, 785);

document.Add(watermark);
document.Open();
PdfContentByte cb = writer.DirectContent;
PdfImportedPage newPage;
int iPageNum = reader.NumberOfPages;
for(int j=1; j<= iPageNum;j++)
{
document.NewPage();
newPage = writer.GetImportedPage(reader,j);
cb.AddTemplate(newPage,0,0);
}
document.Close();
writer.Close();
reader.Close();
}
catch (Exception ex)
{
WriteLog.Log(ex.ToString());
throw ex;
}
}