c# - PDFsharp 1.50 beta 3:向PDF添加密码时所有者密码错误

我正在探索PDFsharp库，并且遇到保护PDF的密码问题。

在他们的网站http://www.pdfsharp.com/PDFsharp/index.php?option=com_content&task=view&id=36&Itemid=47上遵循此示例，

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";

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

document.Save（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)

最佳答案

原来PDFsharp 1.50 beta 3有问题。您的代码没有错。

要快速修复，您可以下载PDFsharp源代码并进行以下更改：

在方法“ void DoSave（PdfWriter writer）”的文件“ PdfDocument.cs”中，查找“ // HACK：Remove XRefTrailer”（在第375行附近）并进行如下更改（7个新行替换了2个旧行）：

// 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。尽管我确实希望新代码的性能永远不会比旧版本差，但并不能保证。

比PDFsharp 1.50 beta 3更高的未来版本的PDFsharp不需要此修补程序。