I don't think org-ref is responsible, except that it installs pdf-tools. When I click on a link like 
[[./2019-07-04.pdf]] it opens in acrobat for me.

I don't have anything fancy
org-file-apps is a variable defined in `org.el'.
Its value is
((auto-mode . emacs) ("\\.mm\\'" . default) ("\\.x?html?\\'" . default)
 ("\\.pdf\\'" . default))

which I guess means on osx that it gets opened with "open".

It looks like you can do this

#+BEGIN_SRC emacs-lisp
(setf (cdr (assoc "\\.pdf\\'" org-file-apps)) "evince %s")
#+END_SRC

to make it open in evince.


John

-----------------------------------
Professor John Kitchin 
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803


On Thu, Jul 4, 2019 at 7:24 AM Joseph Vidal-Rosset <joseph.vidal.rosset@gmail.com> wrote:
Dear Colin (cc. John),

Many thanks ! Unfortunately, I have always the same result. Here is the message:

Viewing with pdf-view-mode
pdf-info-encrypted-p: pdf-info-epdfinfo-program is not executable

is org-ref the culprit? I cc. to John Kitchin.

Best wishes,

Jo.

Le jeu. 4 juil. 2019 à 13:00, Colin Baxter <m43cap@yandex.com> a écrit :
>
> Dear Joseph,
> >>>>> Joseph Vidal-Rosset <joseph.vidal.rosset@gmail.com> writes:
>
>     > Hi the list, I do not want to use pdf-tools to view pdf in emacs,
>     > I want only to use an external program (evince) to view pdf
>     > files. Unfortunately, links to pdf do not work with openwith and
>     > my emacs open on a pdf. I cannot delete pdft-tools that is a
>     > dependency of org-ref that I am using. A solution for my setup
>     > would be welcome.
>
> Try this:
>
> (add-hook 'org-mode-hook
>            '(lambda ()
>             (delete '("\\.pdf\\'" . default) org-file-apps)
>             (add-to-list 'org-file-apps '("\\.pdf\\'" . "evince %s"))))
>
> Best wishes,
>
> Colin Baxter
> www.Colin-Baxter.com