pdf问题关闭选项c#winform

我创建了一个PDF文件，并通过邮件发送，现在我又发送了一次，我收到了这个错误

过程。。。。。因为它正被另一个进程占用

       Document doc = new Document(iTextSharp.text.PageSize.LETTER, 10, 10, 42, 35);  
 try 
 {  
     PdfWriter wri = PdfWriter.GetInstance(doc, new FileStream("c:''Test11.pdf",FileMode.Create));  
     doc.Open;  
      Paragraph paragraph = new Paragraph("This is my first line using Paragraph.");  
     Phrase pharse = new Phrase("This is my second line using Pharse.");  
     Chunk chunk = new Chunk(" This is my third line using Chunk.");  
  doc.Add(paragraph);  
     doc.Add(pharse);  
     doc.Add(chunk);  
 }  
catch (DocumentException dex)  
{  
 }  
 finally 
 {  
     doc.Close(); 
 }