比較經常用的是第二種

  String path = @"X:\xxx\xxx";

            //第一種方法獲取指定格式
            var files = Directory.GetFiles(path, "*.txt");

            foreach (var file in files)
                Console.WriteLine(file);

            //第二種方法獲取指定格式
            DirectoryInfo folder = new DirectoryInfo(path);

            foreach (FileInfo file in folder.GetFiles("*.txt"))
            {
                Console.WriteLine(file.FullName);
            }
             //獲取所有的檔名，不管什麼格式
            DirectoryInfo folder = new DirectoryInfo(path);

            foreach (FileInfo file in folder.GetFiles("*"))
            {
                Console.WriteLine(file.FullName);
            }