aspose.pdf 怎么只能转4页PDF？求指点

Question

 /// <summary>
        /// 将pdf文档转换为图片的方法（该方法基于第三方DLL），你可以像这样调用该方法：
        /// ConvertPDF2Image("F:\\PdfFile.doc", "F:\\", "ImageFile", 1, 20, ImageFormat.Png, 256);
        /// </summary>
        /// <param name="pdfInputPath">Word文件路径</param>
        /// <param name="imageOutputPath">图片输出路径，如果为空，默认值为Word所在路径</param>
        /// <param name="imageName">图片的名字，不需要带扩展名，如果为空，默认值为Word的名称</param>
        /// <param name="startPageNum">从PDF文档的第几页开始转换，如果为0，默认值为1</param>
        /// <param name="endPageNum">从PDF文档的第几页开始停止转换，如果为0，默认值为Word总页数</param>
        /// <param name="imageFormat">设置所需图片格式，如果为null，默认格式为PNG</param>
        /// <param name="resolution">设置图片的像素，数字越大越清晰，如果为0，默认值为128，建议最大值不要超过1024</param>
        public static void ConvertPdfToImage(string wordInputPath, string imageOutputPath,
            string imageName, int startPageNum, int endPageNum, ImageFormat imageFormat, int resolution)
        {
            try
            {
                // open word file

                Aspose.Pdf.Document doc = new Aspose.Pdf.Document(wordInputPath);

                // validate parameter
                if (doc == null) { throw new Exception("Pdf文件无效或者Pdf文件被加密！"); }
                if (imageOutputPath.Trim().Length == 0) { imageOutputPath = Path.GetDirectoryName(wordInputPath); }
                if (!Directory.Exists(imageOutputPath)) { Directory.CreateDirectory(imageOutputPath); }
                if (imageName.Trim().Length == 0) { imageName = Path.GetFileNameWithoutExtension(wordInputPath); }
                if (startPageNum <= 0) { startPageNum = 1; }
                if (endPageNum > doc.Pages.Count || endPageNum <= 0) { endPageNum = doc.Pages.Count; }
                if (startPageNum > endPageNum) { int tempPageNum = startPageNum; startPageNum = endPageNum; endPageNum = startPageNum; }
                if (imageFormat == null) { imageFormat = ImageFormat.Png; }
                if (resolution <= 0) { resolution = 128; }

                //PdfSaveOptions pdfSaveOptions = new PdfSaveOptions();
                //pdfSaveOptions.SaveFormat= GetSaveFormat(imageFormat);

                ImageSaveOptions imageSaveOptions = new ImageSaveOptions(GetSaveFormat(imageFormat));

                imageSaveOptions.Resolution = resolution;

                // start to convert each page
                for (int i = startPageNum; i <= endPageNum; i++)
                {
                    imageSaveOptions.PageIndex = i - 1;

                    MemoryStream stream = new MemoryStream();
                    Aspose.Pdf.SaveOptions pdfSaveOptions = new Aspose.Pdf.PdfSaveOptions();
                    //Aspose.Pdf.Devices.Resolution reso = new Aspose.Pdf.Devices.Resolution(resolution);
                    Aspose.Pdf.Devices.PngDevice pngDevice = new Aspose.Pdf.Devices.PngDevice(990, 1400);

                    string strNumber;
                    if (i < 10)
                    {
                        strNumber = "0" + i.ToString();
                    }
                    else
                    {
                        strNumber = i.ToString();
                    }
                    pngDevice.Process(doc.Pages[i], Path.Combine(imageOutputPath, imageName) + "_" + strNumber + "." + imageFormat.ToString());
                    stream.Dispose();
                    //doc.Save(Path.Combine(imageOutputPath, imageName) + "_" + strNumber + "." + imageFormat.ToString(), pdfSaveOptions);
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

Aspose.Pdf.Document doc = new Aspose.Pdf.Document(wordInputPath)；调试的时候，发现刚进来到这里，doc.page.count是pdf的页数没毛病，但是doc.pages就只有4页。想不通。。其他代码都还没执行，第一行就这样，这是因为我的aspose是免费版的缘故吗？如果不是那可能是什么原因呢？刚刚接触Aspose和.net，所以来问问，大神help~~~

Answer 1

得到PDF的路径之后，根据PDF转换为图片时只能转换4页的内容