public String Upload()
        {
            var fileName = Path.GetFileNameWithoutExtension(Request.Files[0].FileName);
            string extension = System.IO.Path.GetExtension(Request.Files[0].FileName);

            if (Request.Files.Count > 0 && extension == ".pdf")
            {
                Request.Files[0].SaveAs(Server.MapPath("/Content/userfiles/wholesale/") + FilenameFromTitle(fileName, extension));
                return "1";
            }

            else
            {
                return "0";
            }  
        }

        public static string FilenameFromTitle(string name, string extension)
        {
            DateTime time = DateTime.Now;
            string format = "MMddyy_HHmmss";
            //Console.WriteLine(time.ToString(format));

            // first trim the raw string
            string safe = name.Trim();

            // replace spaces with hyphens
            safe = safe.Replace(" ", "-").ToLower();

            // replace any 'double spaces' with singles
            if(safe.IndexOf("--") > -1)
                while(safe.IndexOf("--") > -1)
                    safe = safe.Replace("--", "-");

            // trim out illegal characters
            safe = Regex.Replace(safe, "[^a-z0-9\\-]", "");
            

            // trim the length
            if(safe.Length > 50)
                safe = safe.Substring(0, 49);

            // clean the beginning and end of the filename
            char[] replace = {'-','.'};
            safe = safe.TrimStart(replace);
            safe = safe.TrimEnd(replace);
            safe = safe.ToLower() + "_" + time.ToString(format) + extension;
            //safe = safe.ToLower() + extension;

            return safe;
        }

C# File upload with safe filename

C#