Can't release file in asp.net MVC on IIS

Question

Here's the function i made :

if (Valide())
{
    try
    {
        File.Delete(Server.MapPath("F16client.pdf"));
    }
    catch
    {
    }

    using (FileStream ms = new FileStream(Server.MapPath("F16client.pdf"), FileMode.Create, FileAccess.Write, FileShare.None))
    {
        PdfReader lecteur = new PdfReader(Server.MapPath("~/Formulaires/f16.pdf"));

        PdfStamper etampeur = new PdfStamper(lecteur, ms);

        // DO STUFF, Whatever

        etampeur.FormFlattening = true;
        etampeur.Close();
        lecteur.Close();

        System.Net.Mail.Attachment at = new Attachment(Server.MapPath("F16client.pdf"));                                            
    }
}

It work when testing local, but on IIS, this W3W process won't let go of my f16client.pdf and i always end up with :

The process cannot access the file 'D:\inetpub\wwwroot\Formulaire16\F16client.pdf' because it is being used by another process.

Why is that file still in use when on IIS and not when testing local ??????

Answer 1

Well... no magic here. Thanks to Feryal Badili for pointing out the problem, an email attachement is something that actually holds the ressource...

So, a simple :

    at.Dispose();

before the end of the function and alls good. Yeah...

The reason why it worked on local is probably because i was pushing the stop everything button everytime i tested, and therefore, i was killing the handle everytime it tried my function.