如何制作可下载的正确pdf文件，并在 asp.net 的itextsharp中对其进行验证

我使用itextsharp创建了一个PDF文件，它工作正常。我创建了一个 Activex 控件，用于在客户端使用 USB 令牌对 PDF 文件进行数字签名。客户端使用其USB令牌对PDF文件进行数字签名，并将PDF文件存储到服务器上，其他授权人员可以下载它。Activex只是获取一个PDF文件，并对PDF文件进行数字签名并临时存储，然后使用itextsharp库的PdfEncodings类将PDF文件作为base64字符串返回。为了使用 Activex 对象，我创建了两个 asp.net 隐藏字段，一个用于未签名的字段，另一个用于签名的 PDF。创建 PDF 文件后，我将其转换为 base64 字符串，然后将其分配给 asp.net 隐藏字段，然后调用 javascript 函数使用 Activex 控件进行签名，然后将值分配给另一个 asp.net 隐藏字段，然后获取该值并使其可下载，但是，当下载 PDF 时，它说 PDF 已损坏。我已经检查了临时文件夹中的PDF文件，这是正确的。

用于在 activex 控件中对 pdf 进行数字签名的代码

PdfReader pdfReader = new PdfReader(PdfEncodings.ConvertToBytes(unsignedPDF, null));
        string fileName = System.IO.Path.GetTempPath() + Guid.NewGuid().ToString() + ".pdf";
        FileStream signedPdf = new FileStream(fileName, FileMode.Create);
        PdfStamper pdfStamper = PdfStamper.CreateSignature(pdfReader, signedPdf, ''0');
        X509Store store = new X509Store(StoreLocation.CurrentUser);
        store.Open(OpenFlags.ReadOnly);
        X509Certificate2Collection collection = (X509Certificate2Collection)store.Certificates;
        X509Certificate2Collection sel = X509Certificate2UI.SelectFromCollection(store.Certificates, null, null, X509SelectionFlag.SingleSelection);
        if (sel.Count > 0)
        {
            X509Certificate2 cert = sel[0];
            Org.BouncyCastle.X509.X509CertificateParser cp = new Org.BouncyCastle.X509.X509CertificateParser();
            Org.BouncyCastle.X509.X509Certificate[] chain = new Org.BouncyCastle.X509.X509Certificate[] { cp.ReadCertificate(cert.RawData) };
            IExternalSignature externalSignature = new X509Certificate2Signature(cert, "SHA-1");
            PdfSignatureAppearance signatureAppearance = pdfStamper.SignatureAppearance;
            signatureAppearance.Reason = "I declare this document is legal";
            signatureAppearance.Location = "Delhi";
            signatureAppearance.SetVisibleSignature(new iTextSharp.text.Rectangle(100, 100, 250, 150), pdfReader.NumberOfPages, "Signature");
            signatureAppearance.SignatureRenderingMode = PdfSignatureAppearance.RenderingMode.DESCRIPTION;
            MakeSignature.SignDetached(signatureAppearance, externalSignature, chain, null, null, null, 0, CryptoStandard.CMS);
            return PdfEncodings.ConvertToString(File.ReadAllBytes(fileName), null);
        }
        else
        {
            return "ERROR";
        }

从浏览器下载PDF的代码：

byte[] pdfByte = PdfEncodings.ConvertToBytes(signed.Value, null);
        Response.Clear();
        MemoryStream ms = new MemoryStream(pdfByte);
        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=labtest.pdf");
        Response.Buffer = true;
        ms.WriteTo(Response.OutputStream);
        Response.End();