ASP.Net文件中包含iTextSharp命名空间时，ApiController.cs Web API返回500内部服务器错误

using System.IO;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using iTextSharp.text;
using iTextSharp.text.pdf;

public class PdfController : ApiController
{
    [HttpGet]
    public HttpResponseMessage GetPdf()
    {
        try
        {
            // 创建内存中的PDF文档
            var document = new Document();
            var stream = new MemoryStream();
            PdfWriter.GetInstance(document, stream);
            document.Open();

            // 添加内容到PDF
            document.Add(new Paragraph("Hello World"));

            // 关闭文档
            document.Close();

            // 设置HTTP响应
            var response = Request.CreateResponse(HttpStatusCode.OK);
            response.Content = new StreamContent(stream);
            response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
            response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
            {
                FileName = "HelloWorld.pdf"
            };

            return response;
        }
        catch (Exception ex)
        {
            // 处理异常
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, ex);
        }
    }
}