C#检测两个文件内容是否相同

不知道为什么对Excel 2010 xlsx后缀的文件没有效果，求解！

对其他文件有效，如.txt,.csv

 using System;
 using System.Security.Cryptography;
 using System.IO;

 namespace CheckFile
 {
     class Program
     {
         static void Main(string[] args)
         {
             string filePath1 = @"D:/1.txt";
             string filePath2 = @"D:/2.txt";
             bool result = CheckFile(filePath1, filePath2);
             Console.WriteLine(result.ToString());
             Console.ReadKey();

         }
         /// <summary>
         /// Check File
         /// </summary>
         /// <param name="filePath1"></param>
         /// <param name="filePath2"></param>
         /// <returns></returns>
         public static bool CheckFile(string filePath1, string filePath2)
         {
             using (HashAlgorithm hash = HashAlgorithm.Create())
             {
                 using (FileStream file1 = new FileStream(filePath1, FileMode.Open, FileAccess.Read)
                     , file2 = new FileStream(filePath2, FileMode.Open, FileAccess.Read))
                 {
                     byte[] hashByte1 = hash.ComputeHash(file1);
                     byte[] hashByte2 = hash.ComputeHash(file2);
                     string str1 = BitConverter.ToString(hashByte1);
                     string str2 = BitConverter.ToString(hashByte2);
                     return (str1 == str2);
                 }
             }
         }
     }
 }