PDF文件转换BMP文件

把PDF文件格式转换为BMP格式
 Image emf = doc.SaveAsImage(0, Spire.Pdf.Graphics.PdfImageType.Metafile);
            Image zoomImg = new Bitmap((int)(emf.Size.Width * 2), (int)(emf.Size.Height * 2));

            using (Graphics g = Graphics.FromImage(zoomImg))

            {

                g.ScaleTransform(2.0f, 2.0f);

                g.DrawImage(emf, new Rectangle(new Point(0, 0), emf.Size), new Rectangle(new Point(0, 0), emf.Size), GraphicsUnit.Pixel);

            }