Akasha or Geth may be denying access to open URLs in evince PDF viewer.

[jamesray1]

Please read this: https://askubuntu.com/questions/997511/how-to-open-a-link-in-a-pdf-with-the-error-unable-to-open-external-link-faile#997511. I think Akasha or Geth is denying the evince PDF viewer in Ubuntu 17.10 from opening links, but maybe not.