使用itextsharp组件剪切PDF文件输出流文件

public static byte[] CropPdf(float llx,
            float lly,
            float urx,
            float ury,
            byte[] fileData)
        {
            PdfReader reader = new PdfReader(fileData);
            int n = reader.NumberOfPages;
            PdfDictionary pageDict;
            PdfRectangle rect = new PdfRectangle(llx, lly, urx, ury);
            for (int i = 1; i <= n; i++)
            {
                pageDict = reader.GetPageN(i);
                pageDict.Put(PdfName.CROPBOX, rect);
            }
            using (MemoryStream ms = new MemoryStream())
            {
                using (PdfStamper stamper = new PdfStamper(reader, ms))
                {
                }
                return ms.ToArray();
            }
        }

---