如何使用 GhostScript 在 ASP.NET Web应用程序中显示PDF:报错

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Web;
using Cyotek.GhostScript.PdfConversion;

namespace GhostScriptWebTest
{
  public class PdfImage : IHttpHandler
  {
    public void ProcessRequest(HttpContext context)
    {
      string fileName;
      int pageNumber;
      Pdf2Image convertor;
      Bitmap image;

      fileName = context.Server.MapPath("~/" + context.Request.QueryString["fileName"]);
      pageNumber = Convert.ToInt32(context.Request.QueryString["page"]);

      // convert the image
      convertor = new Pdf2Image(fileName);
      image = convertor.GetImage(pageNumber);

      // set the content type
      context.Response.ContentType = "image/png";

      // save the image directly to the response stream
      image.Save(context.Response.OutputStream, ImageFormat.Png);
    }

    public bool IsReusable
    { get { return true; } }
  }
}

using System;
using System.Collections.Specialized;
using System.Web;
using Cyotek.GhostScript.PdfConversion;

namespace GhostScriptWebTest
{
  public partial class _Default : System.Web.UI.Page
  {
    protected void previousLinkButton_Click(object sender, EventArgs e)
    {
      this.IncrementPage(-1);
    }

    protected void nextLinkButton_Click(object sender, EventArgs e)
    {
      this.IncrementPage(1);
    }

    private void IncrementPage(int increment)
    {
      NameValueCollection queryString;
      int pageNumber;
      string pdfFileName;
      Pdf2Image converter;

      queryString = HttpUtility.ParseQueryString(pdfImage.ImageUrl.Substring(pdfImage.ImageUrl.IndexOf("?")));
      pdfFileName = queryString["fileName"];
      pageNumber = Convert.ToInt32(queryString["page"]) + increment;
      converter = new Pdf2Image(this.Server.MapPath("~/" + pdfFileName));

      if (pageNumber > 0 && pageNumber <= converter.PageCount)
        pdfImage.ImageUrl = string.Format("~/PdfImage.ashx?fileName={0}&page={1}", pdfFileName, pageNumber);
    }
  }
}