How can manage length of text in C#

 #region DisplayAbout_book()
    public string DisplayAbout_book(object DataItem)
    {
        string About_book = Convert.ToString(DataBinder.Eval(DataItem, "About_book"));
        if (About_book != string.Empty)
        {
            if (About_book.Length > 75)
            {
                About_book = About_book.ToString().Substring(0, 75);
            }
            else
            {
                About_book = About_book.ToString();
            }
        }
        return About_book;
    }
    #endregion