UnityEditor.EditorUtility.OpenWithDefaultApp C# (CSharp) Method

        public static extern void OpenWithDefaultApp(string fileName);
        private static void Private_DisplayCustomMenu(Rect screenPosition, string[] options, int[] enabled, int[] separator, int[] selected, SelectMenuItemFunction callback, object userData, bool showHotkey)

        protected static void OpenProject()
        {
            path = string.Format("{0}/Hotfix~/Hotfix.sln", PATH);

            EditorUtility.OpenWithDefaultApp(path);
        }