How to remove commonly occuring English words from a string

I’m using this function to filter common words out of a search query.

protected string removeCommonWords(string sourceStr)
{
    string[] seperator = { " " };
    string[] ignoreWords = { "a", "all", "am", "an", "and", "any", "are", "as",
        "at", "be", "but", "can", "did", "do", "does", "for", "from", "had",
        "has", "have", "here", "how", "i", "if", "in", "is", "it", "no", "not",
        "of", "on", "or", "so", "that", "the", "then", "there", "this", "to",
        "too", "up", "use", "what", "when", "where", "who", "why", "you" };
    string[] outputStr = { };

    outputStr = sourceStr.ToLower().Split(seperator, StringSplitOptions.RemoveEmptyEntries);

    foreach (string unwantedWord in ignoreWords)
    {
        int index = Array.IndexOf(outputStr, unwantedWord);

        if (index != -1)
        {
            string[] copyStrArr = new string[outputStr.Length - 1];

            // copy the elements before the found index
            for (int i = 0; i < index; i++)
            {
                copyStrArr[i] = outputStr[i];
            }

            // copy the elements after the found index
            for (int i = index; i < copyStrArr.Length; i++)
            {
                copyStrArr[i] = outputStr[i + 1];
            }

            outputStr = copyStrArr;
        }
    }

    sourceStr = string.Join(" ", outputStr);

    return sourceStr;
}

Let me know if you guys have a better solution.