The page you mentioned saved me, thanks!
Here is how:
As they indicate, what is needed is to configure fontconfig
. I can't be sure for Ubuntu, but for Debian this means creating or editing this file :
/etc/fonts/local.conf
For the font substitution, you just need to include something like this example:
<alias>
<family>Helvetica</family>
<accept><family>Nimbus Sans L</family></accept>
</alias>
Where the Helvetica family would be substituted by the 'Nimbus Sans L' family.
To check that it works, you may use a PDF file containing e.g. Helvetica, and type:
pdffonts -subst <yourfile>.pdf
This will list the fonts substitutions. In my case, it worked just fine, with poppler now doing the right substitution.