Random numbers in C#

int randomNumber(int min, int max)
{
 Random rd = new Random()
 return rd.Next(min,max);
}

Method will return a number from min to max

private void button2_Click(object sender, EventArgs e)
{
    // Generate the "IV" and the salt for the password
    RandomNumberGenerator rng = RandomNumberGenerator.Create();
    byte[] IV = new byte[16];
    byte[] salt = new byte[16];
    rng.GetNonZeroBytes(IV);
    rng.GetNonZeroBytes(salt);
    // Hash the password
    Rfc2898DeriveBytes passwordHasher = new Rfc2898DeriveBytes(_password, salt);
    byte[] key = passwordHasher.GetBytes(16);
    Rijndael rijndaal = new RijndaelManaged();
    rijndaal.IV = IV;
    rijndaal.Key = key;
    using (FileStream input = File.Open(_fileName, FileMode.Open))
    {
        using (StreamReader reader = new StreamReader(input))
        {
            using (FileStream output = File.Create(_fileName + ".crypted"))
            {
                using (CryptoStream encryptingStream =
                    new CryptoStream(output, rijndaal.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    // first write the salt and the IV
                    output.Write(salt, 0, 16);
                    output.Write(IV, 0, 16);
                    output.Flush();
                    using (StreamWriter writer = new StreamWriter(encryptingStream))
                    {
                        writer.Write(reader.ReadToEnd());
                    }
                }
            }
        }
    }
}