How to search text within files and directories?

static string[] keywords = {"a", "restricted", "the"};

static void Main(string[] args)
{
    search_file(@"D:\Documents", keywords);
    Console.ReadKey();
}
static void search_file(string path, string[] keywords)
{
    var files = Directory.EnumerateFiles(path, "*.*", SearchOption.AllDirectories);
    Console.WriteLine("Files count: {0}", files.Count().ToString());
    string Content = string.Empty;

    foreach (string file in files)
    {
        switch (System.IO.Path.GetExtension(file))
        {
            case ".txt":
                Content = GetFileText(file);
                SearchForContent(Content, file);
                break;

            case ".pdf":
                Content = GetTextFromPDF(file);
                SearchForContent(Content, file);
                break;

            case ".docx":
                Content = GetTextFromWord(file);
                SearchForContent(Content, file);
                break;
        }

    }
}
static void SearchForContent(string Contents, string file)
{
    foreach (string key in keywords)
    {
        if (Contents.Contains(key))
        {
            Console.WriteLine("key: " + key + " " + file);
        }
    }
}

static string GetFileText(string name)
{
    string fileContents = String.Empty;

    // If the file has been deleted since we took
    // the snapshot, ignore it and return the empty string.
    if (System.IO.File.Exists(name))
    {
        fileContents = File.ReadAllText(name);
    }
    return fileContents;
}
static string GetTextFromPDF(string path)
{
    PdfReader reader = new PdfReader(path);
    using (StringWriter output = new StringWriter())
    {

        for (int i = 1; i <= reader.NumberOfPages; i++)
        {
            output.WriteLine(PdfTextExtractor.GetTextFromPage(reader, i, new SimpleTextExtractionStrategy()));
        }
        reader.Close();

        return output.ToString();
    }
}
static string GetTextFromWord(string direct)
{
    StringBuilder text = new StringBuilder();
    Microsoft.Office.Interop.Word.Application word = new Microsoft.Office.Interop.Word.Application();
    object miss = System.Reflection.Missing.Value;
    object path = direct;
    object readOnly = true;
    Microsoft.Office.Interop.Word.Document docs = word.Documents.Open(ref path, ref miss, ref readOnly, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss);

    for (int i = 0; i < docs.Paragraphs.Count; i++)
    {
        text.Append(" \r\n " + docs.Paragraphs[i + 1].Range.Text.ToString());
    }

    return text.ToString();
}