public static string iso8859ToUnicode(string src) {

        Encoding iso = Encoding.GetEncoding("iso8859-1");

        Encoding unicode = Encoding.UTF8;

        byte[] isoBytes = iso.GetBytes(src);

        byte[] unibytes = Encoding.Convert(iso,unicode,isoBytes);

        char[] unichars = new char[iso.GetCharCount(unibytes,0,unibytes.Length)];

        unicode.GetChars(unibytes,0,unibytes.Length,unichars,0);

        return new string(unichars);

    }

public static void ConvertLatin1ToUtf8(string inputFile, string outputFile)
{
    Encoding latin1 = Encoding.GetEncoding(28591);
    string text = File.ReadAllText(inputFile, latin1);
    File.WriteAllText(outputFile, text, Encoding.UTF8);
}

public static void ConvertLatin1ToUtf8(string inputFile, string outputFile)
{
    Encoding latin1 = Encoding.GetEncoding(28591);
    byte[] latinBytes = File.ReadAllBytes(inputFile);
    byte[] utf8Bytes = Encoding.Convert(latin1, Encoding.UTF8, latinBytes);
    File.WriteAllBytes(outputFile, utf8Bytes);
}

unicode.GetString(unibytes);