how upload pdf file mime type in javascript [Resolved]

I am developing an app where a user uploads PDF files to the server, via a FileUpload control.

As part of the usual security/reliability checks I wanted to verify that the uploaded document was actually
a PDF, not just say, a Text file renamed to have a .PDF extension. Now i want in javascript. means client site.

protected void Button1_Click(object sender, EventArgs e)
    {
        System.IO.BinaryReader r = new System.IO.BinaryReader(FileUpload2.PostedFile.InputStream);
        string fileclass = "";
        byte buffer;
        try
        {
            buffer = r.ReadByte();
            fileclass = buffer.ToString();
            buffer = r.ReadByte();
            fileclass += buffer.ToString();
        }
        catch
        {
        }
        r.Close();
        if(fileclass!=“3780”)
        {
            ltl_status.Text = "<p>Error - The upload file must be in PDF format.</p>"
            return;
        }
    }

[Resolved]