Thanks, Ihor.

That change worked.

(when (eq system-type 'windows-nt)

  (setq org-file-apps

        '((\\.\\(docx\\|doc\\)\\' . system)

          (\\.\\(xlsx\\|xls\\)\\' . system)

          (\\.\\(pdf\\)\\' . system)

          (\\.\\(pptx\\|ppt\\)\\' . system)

          (auto-mode . emacs))))