var envDteType = Type.GetTypeFromProgID("VisualStudio.DTE.15.0");

        var envDte = Activator.CreateInstance(envDteType, true);
        var dte2 = (DTE2)envDte;

        var solution = (Solution4)dte2.Solution;
        solution.Open(filename);

        // execute various tasks

        solution.Close();
        // how to dispose of dte2?