title: c# check the extension of the uploaded file
body: <p>I am looking for a simple way to check the extension of the uploaded file,  if it was PDF file do something, else a warning message will show that its (wrong file type), but the problem with my code is if I selected any file type instead of PDF it will show the error page with this message:</p>
  
  <pre><code>   Server Error in '/' Application.
     PDF header signature not found.
     Exception Details: iTextSharp.text.exceptions.InvalidPdfException: PDF header signature not found.
  
  
  
          &lt;asp:FileUpload runat="server" ID="file1" AllowMultiple="true" /&gt;
  
  
          string fileName = Path.GetFileName(file1.FileName);
          FileInfo fi = new FileInfo(fileName);
          string ext = fi.Extension;
  
          if (ext == ".pdf")
          {
          //do something
          }
          else
          Label1.Text = string.Format("wrong file type");
  </code></pre>