ITextsharp在使用線條或矩形時使簽名無效

Question

當我使用ITextSharp對已使用此代碼進行數字簽名的文檔進行數字簽名時，會使其他簽名無效。如果我使用文字或圖片進行數字簽名，它可以正常工作。這是Adobe/Itextsharp限制還是代碼有問題？

public void SignWithLine(string pdfFilePath, string outputFilePath, LineAnnotation lineAnnotation) 
{   
    double xStartPoint = 89.285969238281268, yStartPoint = 343.08978515624881, xEndPoint = 72.7515234375, yEndPoint = 496.03341796874878, lineStroke = .24; 

    CertificateWrapper certificate = CertificateWrapper.GetCertificateInformationFromSignature(GetCertificateInformation()); 
    PdfReader reader = new PdfReader(pdfFilePath); 
    PdfTemplate layer = null; 
    using (PdfStamper signature = PdfStamper.CreateSignature(reader, null, '\0', outputFilePath, true)) 
    { 
     PdfSignatureAppearance signatureAppearance = signature.SignatureAppearance; 
     signatureAppearance.SignatureRenderingMode = PdfSignatureAppearance.RenderingMode.GRAPHIC; 
     Rectangle rect = new Rectangle((float)Math.Min(xStartPoint, xEndPoint), (float)Math.Min(yStartPoint, yEndPoint), (float)Math.Min(xStartPoint, xEndPoint) + (float)Math.Abs(xEndPoint - xStartPoint), (float)Math.Min(yStartPoint, yEndPoint) + (float)Math.Abs(yEndPoint - yStartPoint)); 
     signatureAppearance.SetVisibleSignature(rect, lineAnnotation.PageIndex + 1, GetCertificateFieldName()); 
     layer = signatureAppearance.GetLayer(2); 

     PdfContentByte cb = signature.GetUnderContent(lineAnnotation.PageIndex + 1); 
     cb.SetLineWidth((float)lineStroke); 
     cb.MoveTo((float)xStartPoint, (float)yStartPoint); 
     cb.LineTo((float)(xEndPoint), (float)(yEndPoint)); 
     cb.Stroke(); 

     signatureAppearance.CertificationLevel = PdfSignatureAppearance.NOT_CERTIFIED; 
     // Normal signature, not a certification 
     MakeSignature.SignDetached(signatureAppearance, certificate.DigitalSignature, certificate.Chain, null, null, null, 0, true); 

     signature.Close(); 
    } 
} 

Answer 1

signature是您的PdfStamper。您在

上畫一條線

PdfContentByte cb = signature.GetUnderContent(lineAnnotation.PageIndex + 1); 

即，您將其繪製在頁面的內容流中。這被視爲頁面內容的改變，因此被原始簽名禁止。有關允許更改的詳細信息，請參閱this answer。

Answer 2

我找到了一種通過修改iTextSharp庫來實現這個功能的方法。

//首先我重載SetVisibleSignature通過INT

公共無效SetVisibleSignature的列表（矩形pageRect，字符串fieldName的，列表分頁） { 頁=分頁; //頁面是私人列表頁面; ... }

//其次，在PreClose事件中，你更新如下圖所示

  sigField.Page = pagen; 
      if (pagen != 0) 
       writer.AddAnnotation(sigField, pagen); 
      else if (pages != null && pages.Count > 0) 
       pages.ForEach(f => writer.AddAnnotation(sigField, f)); // this annotates all pages with the same signature 
      else 
       throw new DocumentException("No pages specified for signature.");