The fix for transparency did not work

[OrionRandD]

(defun my-fix-pdf-selection ()
"Replace pdf with one where selection shows transparently."
(interactive)
(unless (equal (file-name-extension (buffer-file-name)) "pdf")
(error "Buffer should visit a pdf file."))
(unless (equal major-mode 'pdf-view-mode)
(pdf-view-mode))
;; save file in QDF-mode
(qpdf-run (list
(concat "--infile="
(buffer-file-name))
"--qdf --object-streams=disable"
"--replace-input"))
;; do replacements
(text-mode)
(read-only-mode -1)
(while (re-search-forward "3 Tr" nil t)
(replace-match "7 Tr" nil nil))
(save-buffer)
(pdf-view-mode))

=> When I eval the function, I get:
=> Symbol’s function definition is void: qpdf-run

:(