如何使用C#加密/解密.xlsx/.doc文件

我正在为Encrtpt/Decrypt文件编写一个应用程序，并为此使用DESCryptoServiceProvider。这似乎适用于文本文件，但当我对.xlsx文件使用相同的应用程序时，生成的加密文件和解密文件会损坏，我无法再打开它。有什么方法可以加密/解密不同类型的文件，如.doc.xls等吗

更新：添加了加密/解密的代码

public static  void EncryptFile(string filepath,string fileOutput, string key)
    {
        FileStream fsInput = new FileStream(filepath, FileMode.Open, FileAccess.Read);
        FileStream fsEncrypted = new FileStream(fileOutput, FileMode.Create, FileAccess.Write);
        DESCryptoServiceProvider DESc = new DESCryptoServiceProvider();
        DESc.Key = ASCIIEncoding.ASCII.GetBytes(key);
        DESc.IV = ASCIIEncoding.ASCII.GetBytes(key);
        ICryptoTransform desEncrypt = DESc.CreateEncryptor();
        CryptoStream cryptoStream = new CryptoStream(fsEncrypted, desEncrypt, CryptoStreamMode.Write);
        byte[] byteArrayInput = new byte[fsInput.Length - 1];
        fsInput.Read(byteArrayInput, 0, byteArrayInput.Length);
        cryptoStream.Write(byteArrayInput, 0, byteArrayInput.Length);
        cryptoStream.Close();
        fsInput.Close();
        fsEncrypted.Close();
    }
public static void DecryptFile(string filepath, string fileOutput, string key)
    {
        DESCryptoServiceProvider DESc = new DESCryptoServiceProvider();
        DESc.Key = ASCIIEncoding.ASCII.GetBytes(key);
        DESc.IV = ASCIIEncoding.ASCII.GetBytes(key);
        FileStream fsread = new FileStream(filepath, FileMode.Open, FileAccess.Read);
        ICryptoTransform desDecrypt = DESc.CreateDecryptor();
        CryptoStream cryptoStreamDcr = new CryptoStream(fsread, desDecrypt, CryptoStreamMode.Read);
        StreamWriter fsDecrypted = new StreamWriter(fileOutput);
        fsDecrypted.Write(new StreamReader(cryptoStreamDcr).ReadToEnd());
        fsDecrypted.Flush();
        fsDecrypted.Close();
    }
static void Main(string[] args)
    {
        EncryptFile(@"C:'test1.xlsx", @"c:'test2.xlsx", "ABCDEFGH");
        DecryptFile(@"C:'test2.xlsx", @"c:'test3.xlsx", "ABCDEFGH");
    }