>From VFP, I want to Print 3 PDF files in succession to a printer which is not the currently set default printer.
>Notes:
>ShellExecute appears to only print to the default printer.
>Using ShellExecute, if I reset the default Printer and Print the 3 files, then when I restore the default printer to the original printer name, before the printer has not completed it's 3 jobs then I find that the last copies go to the wrong printer.
>Using the SET PRINTER TO command has no effect when Printing via Shell Execute

Not necessarily. It will if a registry entry doesn't exist for the Print verb. Check your registry for the following key:
HKEY_CLASSES_ROOT\.PDF\Shell\Print\Command

It should have a reference to the Acrobat printer.