I use emacs-28, eww use mailcap to open pdf, custom it by open with pdf-tools:
'((type . "application/pdf")
(viewer . pdf-view-mode)))
See Emacs - Help - pdf
viewer for more information.
I just want to shortly explain how I did it while using use-package and how it should probably work for anybody.
On a terminal:
brew install poppler automake
Then in emacs run the following:
; This goes into your emacs config file
(setq pdf-info-epdfinfo-program "/usr/local/bin/epdfinfo"))
;; this only has ...