MemoryStream看起来像使用iTextSharp损坏了文件

I have two codes:

我有两个代码：

string fileInput = @"c:\temp\input.pdf";
string fileOutput = @"c:\temp\saida.pdf";

PdfReader reader = new PdfReader(fileInput);

Stream output = new System.IO.FileStream(fileOutput, System.IO.FileMode.Create);

Document doc = new Document();
PdfCopy writer = new PdfCopy(doc, output);

doc.Open();
PdfImportedPage pagina = writer.GetImportedPage(reader, 23);
writer.AddPage(pagina);

doc.Close();

output.Close();
string fileInput