Set default pdf reader

Edit file : ~/.config/mimeapps.list and set pdf to evince.desktop Works for me. Source: https://askubuntu.com/questions/591425/why-do-pdf-documents-open-with-imagemagick

You can check the file defaults.list and change it to evince if necessary. On my system:

$ cat /usr/share/applications/defaults.list  | grep pdf
application/pdf=evince.desktop;atril.desktop