c# - PDFsharp 1.50 测试版 3 : Empty owner password error when adding password to PDF

Question

我正在探索 PDFsharp 库，但在密码保护 PDF 时遇到问题。

按照他们网站上的这个例子 http://www.pdfsharp.com/PDFsharp/index.php?option=com_content&task=view&id=36&Itemid=47 ,

这是我的代码

 try
 {
   string filename = "hi.pdf";
   File.Copy(Path.Combine("C:/User/Ichigo/Desktop", filename),
   Path.Combine(Directory.GetCurrentDirectory(), filename), true);

   PdfDocument document = PdfReader.Open(filename, "some text");

   PdfSecuritySettings securitySettings = document.SecuritySettings;

   securitySettings.UserPassword="user";
   securitySettings.OwnerPassword="owner";

   securitySettings.PermitAccessibilityExtractContent = false;
   securitySettings.PermitAnnotations = false;
   securitySettings.PermitAssembleDocument = false;
   securitySettings.PermitExtractContent = false;
   securitySettings.PermitFormsFill = true;
   securitySettings.PermitFullQualityPrint = false;
   securitySettings.PermitModifyDocument = true;
   securitySettings.PermitPrint = false;

   document.Save(filename);
 }
 catch (Exception e) 
 { throw new Exception("Something went wrong : " + e); }

每当我添加设置密码的代码时:

securitySettings.UserPassword="user";
securitySettings.OwnerPassword="owner";

我得到 System.NullReferenceException: Object reference not set to an instance of an object. 当我到达保存 PDF 的行时

文档.保存(文件名);我也收到错误消息

---- DEBUG ASSERTION FAILED ----
---- Assert Short Message ----
Empty owner password.
---- Assert Long Message ----

   at PdfSharp.Pdf.Security.PdfStandardSecurityHandler.PrepareEncryption() in c:\Users\Ichigo\Downloads\PDFsharp-MigraDocFoundation-1_50-beta3b\PDFsharp\src\PdfSharp\Pdf.Security\PdfStandardSecurityHandler.cs:line 590
   at PdfSharp.Pdf.PdfDocument.DoSave(PdfWriter writer) in c:\Users\Ichigo\Downloads\PDFsharp-MigraDocFoundation-1_50-beta3b\PDFsharp\src\PdfSharp\Pdf\PdfDocument.cs:line 392
   at PdfSharp.Pdf.PdfDocument.Save(Stream stream, Boolean closeStream) in c:\Users\Ichigo\Downloads\PDFsharp-MigraDocFoundation-1_50-beta3b\PDFsharp\src\PdfSharp\Pdf\PdfDocument.cs:line 325
   at PdfSharp.Pdf.PdfDocument.Save(Stream stream) in c:\Users\Ichigo\Downloads\PDFsharp-MigraDocFoundation-1_50-beta3b\PDFsharp\src\PdfSharp\Pdf\PdfDocument.cs:line 352
   at PdfSharp.Pdf.PdfDocument.Save(String path) in c:\Users\Ichigo\Downloads\PDFsharp-MigraDocFoundation-1_50-beta3b\PDFsharp\src\PdfSharp\Pdf\PdfDocument.cs:line 258

为什么会出现这些错误？

编辑 - 这是 System.NullReferenceException 的堆栈跟踪。

Something went wrong : `System.NullReferenceException: Object reference not set to an instance of an object.`     
 at PdfSharp.Pdf.Security.PdfStandardSecurityHandler.SetHashKey(PdfObjectID id)
   at PdfSharp.Pdf.IO.PdfWriter.WriteBeginObject(PdfObject obj)
   at PdfSharp.Pdf.PdfDictionary.WriteObject(PdfWriter writer)
   at PdfSharp.Pdf.PdfPage.WriteObject(PdfWriter writer)
   at PdfSharp.Pdf.PdfDocument.DoSave(PdfWriter writer)
   at PdfSharp.Pdf.PdfDocument.Save(Stream stream, Boolean closeStream)
   at PdfSharp.Pdf.PdfDocument.Save(Stream stream)
   at PdfSharp.Pdf.PdfDocument.Save(String path)

Answer 1

事实证明 PDFsharp 1.50 beta 3 有问题。您的代码没有问题。

要快速修复，您可以下载 PDFsharp 源代码并进行以下更改:

在文件“PdfDocument.cs”中的方法“void DoSave(PdfWriter writer)”中查找“//HACK: Remove XRefTrailer”(第 375 行左右)并像这样更改它(7 行替换 2 行旧行):

// HACK: Remove XRefTrailer
if (_trailer is PdfCrossReferenceStream)
{
    // HACK^2: Preserve the SecurityHandler.
    PdfStandardSecurityHandler securityHandler = _securitySettings.SecurityHandler;
    _trailer = new PdfTrailer((PdfCrossReferenceStream) _trailer);
    _trailer._securityHandler = securityHandler;
}

免责声明:我仅使用 Hi.pdf 和 HelloWorld.pdf 对此进行了测试。虽然我确实希望新代码的表现永远不会比旧版本差，但我不能保证。

PDFsharp 的 future 版本，比 PDFsharp 1.50 beta 3 更新，应该不需要这个补丁。