using static System.Console;

using System;

public class Program {

    public static void Main() {

        var mainStr = "Joaquim Pedro Soares";

        WriteLine(mainStr.Contains("JOA", StringComparison.OrdinalIgnoreCase));

        WriteLine(mainStr.Contains("Quim", StringComparison.OrdinalIgnoreCase));

        WriteLine(mainStr.Contains("PEDRO", StringComparison.OrdinalIgnoreCase));

        WriteLine(mainStr.Contains("PeDro", StringComparison.OrdinalIgnoreCase));

    }

}

​

namespace System {

    public static class StringExt {

        public static bool Contains(this string source, string search, StringComparison comparison) => source.IndexOf(search, comparison) >= 0;

    }

}