ubuntu 無法修改pdf的打開方式

默認用imagemagick打開，用open with修改沒用，ubuntu tweak tool也沒用

You might find this is a more clear answer that worked for me in Ubuntu 15.10:

edit the file ~/.config/mimeapps.list
just remove the lines that associate PDF to imagemagick in the file:
image/pdf=display-im6.desktop
image/pdf=display-im6.q16.desktop;display-im6.desktop;

http://askubuntu.com/questions/591425/why-do-pdf-documents-open-with-imagemagick