Open file in browser without downloading in ASP.Net using C#

I want to open pdf in browser without downloading it but in my code whenever I click on a pdf file to open it ....

it ask to download it here is my code.

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(Request.QueryString["FileName"]))
            {
                string fileName = Request.QueryString["FileName"];
                string filePath = Server.MapPath("~/files/") + fileName;
                string fileExtension = Path.GetExtension(filePath);
               // byte[] bytes=null;
                switch (fileExtension.ToLower())
                {
                    case ".txt":
                        Response.Write(File.ReadAllText(filePath));
                        break;
                    case ".pdf":
                        Response.ContentType = "Application/pdf";
                        Response.ContentType = "\".pdf\", \"application/pdf\"";
                        Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName);
                        Response.WriteFile(filePath);
                        Response.End();