NameToDisplayString.cs

static string NameToDisplayString(string inDisplayName)
{
    //  (?=               # look-ahead: a position followed by...
    //      \p{Lu}\p{Ll}  #   an uppercase and a lowercase
    //  )                 #
    //  |                 # or
    //  (?<=              # look-behind: a position after...
    //      \p{Ll}        #   an uppercase
    //  )                 #
    //  (?=               # look-ahead: a position followed by...
    //      \p{Lu}        #   a lowercase
    //  )                 #
    string[] strings = Regex.Split(inDisplayName, @"(?=\p{Lu}\p{Ll})|(?<=\p{Ll})(?=\p{Lu})");
    StringBuilder sb = new StringBuilder(inDisplayName.Length * 2);

    string[] articles = {"In", "As", "To", "Or", "At", "On", "If", "Be", "By", "The", "For", "And", "With", "When", "From"};

    strings.ToList().ForEach(s =>
    {
        if (!String.IsNullOrEmpty(s))
        {
            sb.Append(articles.Contains(s) ? s.ToLower() : s);

            if (strings.Last() != s)
                sb.Append(' ');
        }
    });

    return sb.ToString();
}