Need some help with GetPrinterDevice

Hello,
I would like to change the call to  GetPrinterDevice like this  
if (GetPrinterDevice(_T("7-PDF Printer"), &hDevNames, &hDevMode))

to a string, but this will not work
if (GetPrinterDevice (PDF_DRUCKER), &hDevNames, &hDevMode))

      
      

       CString str_PDF="7-PDF Printer";

        LPTSTR string = new TCHAR[str_PDF.GetLength()+1];
       _tcscpy(string,str_PDF);
       strcpy(PDF_DRUCKER,string);
 
       if (GetPrinterDevice (PDF_DRUCKER), &hDevNames, &hDevMode))

please let me know
500 points with a solution.
Thank you.
Best regards,
Thomas