C#

namespace Test
{
    /// <summary>
    /// Description of TimeLimitOpen.
    /// </summary>
    public class TimeLimitOpenv02
    {
        
        [DllImport("acad.exe", CallingConvention = CallingConvention.Cdecl,
            EntryPoint = "?acedPostCommand@@YAHPBD@Z")]
        extern static public int acedPostCommand(string cmd);
        private static string[] DwgList;//<---Modification
        public Document NewDoc;
        DocumentCollection DocMan = AcadApp.DocumentManager;
        System.Timers.Timer CountDownTimer;
        private static int cnt = 1; //<---Modification
        //- Constructor: sets up var's etc for this class before use.
        public TimeLimitOpenv02()
        {
            CountDownTimer = new System.Timers.Timer();
            CountDownTimer.Elapsed += new ElapsedEventHandler(CancelCommand);
            CountDownTimer.Interval = 10000;
        }

        ~TimeLimitOpenv02() // <-- Destructor, do clean up here.
        {
            CountDownTimer.Elapsed -= new ElapsedEventHandler(CancelCommand);
        }
        public void CancelCommand(object sender, ElapsedEventArgs e)
        {
            acedPostCommand ("CancelCmd");
            //MessageBox.Show (DocMan.ToString());
            NewDoc = DocMan.MdiActiveDocument;
            //MessageBox.Show ("Testing");
            //MessageBox.Show (cnt.ToString());
            NewDoc.CloseAndDiscard();
            NewDoc = DocMan.Open (DwgList[cnt], true);
            if (NewDoc != DocMan.MdiActiveDocument) {
                DocMan.MdiActiveDocument = NewDoc;
            }
            ++TimeLimitOpenv02.cnt;//You access it by the class name
            if (TimeLimitOpenv02.cnt > TimeLimitOpenv02.DwgList.Length) {
                CountDownTimer.Enabled = false;
                CountDownTimer.Dispose();
            }
            NewDoc.SendStringToExecute ("_.3dorbit", false, false, true);
        }

        [CommandMethod("TestTimer", CommandFlags.Session)]
        public void Main()
        {
            Autodesk.AutoCAD.Windows.OpenFileDialog Dia =
                new Autodesk.AutoCAD.Windows.OpenFileDialog(
                "Select drawings to update Cloud layer", "", "dwg", "",
                Autodesk.AutoCAD.Windows.OpenFileDialog.OpenFileDialogFlags.AllowMultiple);
            Dia.ShowDialog();
            TimeLimitOpenv02.DwgList = Dia.GetFilenames();
            if (DwgList.Length > 1)
            {
                CountDownTimer.Enabled = true;
                Document NewDoc = DocMan.Open (DwgList[0], true);
                if (NewDoc != DocMan.MdiActiveDocument) {
                    DocMan.MdiActiveDocument = NewDoc;
                }
                NewDoc.SendStringToExecute ("_.3dorbit\n", false, false, true);
            }
        }
    }
}

Regards

[DllImport("User32.dll", CharSet=CharSet.Auto)]
private static extern bool SetForegroundWindow(IntPtr hWnd);

foreach(Process P in Process.GetProcesses())
{
    if (P.MainWindowTitle.Length > 0 && P.MainWindowTitle.IndexOf("Autocad") != -1)
    SetForegroundWindow(P.MainWindowHandle);
}

Regards

this.BackgroundImage = Image.FromFile("theme\\red.png"); // use a double-slash to indicate \r does not mean a return character

this.BackgroundImage = Image.FromFile(@"theme\red.png"); // use a @ symbol to indicate a string literal (auto-escapes \ characters)