GetTitle2

public static string GetTitle2(this ModelDoc2 model)
        {
            var extension = string.Empty;

            if (model.GetType() == (int)swDocumentTypes_e.swDocPART)
                extension = ".sldprt";
            else
                extension = ".sldasm";

            var title = model.GetTitle();

            if (System.IO.Path.HasExtension(title))
                return title;
            else
                return $"{title}{extension}";
        }