Excel VSTO Add-in

I am developing a VSTO Add-in for Excel and I want to add a new CustomTaskPane (userAdminTaskPane) to each new opened Excel document by this code and make it visible:

public static void CreateUploadFile(string name)
        {
            string fileName = String.Concat(name, ".txt");
            string filePath = Path.Combine(Properties.Settings.Default.workingDir,fileName);
            File.WriteAllText(filePath, Properties.Resources.UploadTemplate,Encoding.Unicode);
            Globals.ThisAddIn.Application.Workbooks.OpenText(filePath,Excel.XlPlatform.xlMSDOS,1,Excel.XlTextParsingType.xlDelimited,Excel.XlTextQualifier.xlTextQualifierDoubleQuote,false,true);
            mainTaskPane userAdminTaskPane = new mainTaskPane();
        }

How can I do this? should I handle specific events or can I do this for new Excel Documents created using this method only?