输入数据不是一个完整的块

我正试图为标记为安全的PDF做批量PDF解锁。我可以不用密码打开这些文件，但我不能修改它。我的测试PDF可以使用在线工具解锁，所以我想如果用c#编程是可能的。下面是我的示例代码

static void Main(string[] args)
{
    string inputfile = @"V:'rwong'Work Files'Secured PDF'Test_15.PDF";
    string outputfile = @"V:'rwong'Work Files'Secured PDF'Test_15_Unsecured.PDF";
    Decrypt(inputfile, outputfile);
}
private static void Decrypt(string inputFilePath, string outputfilePath)
{
    string EncryptionKey = "MAKV2SPBNI99212";
    using (Aes encryptor = Aes.Create())
    {
        Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
        encryptor.Key = pdb.GetBytes(32);
        encryptor.IV = pdb.GetBytes(16);
        using (FileStream fsInput = new FileStream(inputFilePath, FileMode.Open))
        {
            using (CryptoStream cs = new CryptoStream(fsInput, encryptor.CreateDecryptor(), CryptoStreamMode.Read))
            {
                using (FileStream fsOutput = new FileStream(outputfilePath, FileMode.Create))
                {
                    int data;
                    while ((data = cs.ReadByte()) != -1)
                    {
                        fsOutput.WriteByte((byte)data);
                    }
                }
            }
        }
    }
}

1. 我一直在while ((data = cs.ReadByte()) != -1)上得到错误但我不知道如何修复它。上面写着input data is not a complete block
2. 是否有可能做到我想要达到的目标，浪费我的时间，或者我走错了路。

谢谢!