var regexTest = new Func<string, bool>(i => Regex.IsMatch(i, @"Awesome.File.(Summary)?.[d]+_[d]+.txt", RegexOptions.Compiled | RegexOptions.IgnoreCase));
  var files = Directory.GetFiles(@"c:pathtofolder").Where(regexTest);

string pattern = ".SUMMARY.";
string[] awesomeFiles = System.IO.Directory.GetFiles("path\to\awesomefiles");

        IEnumerable<string> sum_files = from file in awesomeFiles
                                        where file.ToUpper().Contains(pattern)
                                        select file;

        IEnumerable<string> other_files = from file in awesomeFiles
                                        where !file.ToUpper().Contains(pattern)
                                        select file;