C# and unable to close pdf Files methods Load() & Dispose()

I have a list of pdf files in my listBox, I want to use dispose() to release ressources of the system and delete my pdf files in my directory. but I can not and it throw me an exception when I load the file

An unhandled exception of type 'System.Runtime.InteropServices.InvalidComObjectException' occurred in AxInterop.AcroPDFLib.dll


Additional information: COM object that has been separated from its underlying RCW cannot be used.

  void MonMouseClick(object sender, MouseEventArgs e)
        {
            if (lstDoc.SelectedItem != null)
            {
               
                axAcroPDF.LoadFile(lstDoc.SelectedItem.ToString());
               
            }


        }


 void DeleteFiles(string Rep)
        {
            axAcroPDF.Dispose();
            Array.ForEach(Directory.GetFiles(Rep), File.Delete);
        }


 private void Form1_Load(object sender, EventArgs e)
        {
           DeleteFiles(@"c:\\Temp2");
        }


Please Any Help Or Suggestions!  Thanks!