C# PDFsharp 1.50 beta 3：将密码添加到PDF时出现空所有者密码错误

我正在探索PDFsharp库，并且在密码保护PDF时遇到问题

按照他们网站上的这个例子

这是我的密码

 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:对象引用未设置为对象的实例。

当我到达保存PDF的行时

document.Save（文件名）； 我也收到了错误信息

---- 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

为什么我会犯这些错误

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)

---

结果发现PDFsharp 1.50 beta 3存在问题。你的代码没有问题

对于快速修复，您可以下载PDFsharp源代码并进行以下更改：

在方法“void DoSave（PdfWriter writer writer）”中的文件“PdfDocument.cs”中查找“//HACK:Remove xreftrail”（第375行附近），并将其更改为这样（7行新行替换2行旧行）：

免责声明：我仅使用Hi.pdf和HelloWorld.pdf对其进行了测试。虽然我真的希望新代码永远不会比旧版本表现得更糟，但这并不能保证

---

PDFsharp的未来版本（比PDFsharp 1.50 beta 3更新）不需要此修补程序。

您只会收到一条错误消息：“System.NullReferenceException”。您不会显示该错误的堆栈跟踪。是否所有PDF文件都会出现此错误，例如示例代码附带的HelloWorld.PDF？如果没有，请提供您的Hi.pdf以使错误重现。您是否在错误消息之后收到断言消息？必须首先调查显示first的消息。我不认为要检查pdf，正如您所怀疑的，HelloWorld.pdf中不会出现错误。这里是Hi.pdf。我在错误消息之前得到断言消息。

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