Add timestamp to filename

Extensions.cs

    public static class Extensions
    {

        /// <summary>
        /// Add a timestamp to the filename, before the extension.
        /// </summary>
        /// <param name="fileName">any filename for which you want to add a timestamp, including file extension.</param>
        /// <returns>filename with added timestamp</returns>
        /// <example>
        /// <c>var file = "myfile.txt".AddTimeStamp();</c>
        /// This would return the filename "myfile__20160201120840492.txt"
        /// </example>
        public static string AddTimeStamp(this string fileName)
        {
            return string.Concat(
                Path.GetFileNameWithoutExtension(fileName),
                DateTime.Now.ToString("_yyyyMMddHHmmssfff"),
                Path.GetExtension(fileName)
                );
        }
    }