/usr/share/doc/texlive-doc/latex/expl3/expl3.pdf is in texlive-latex3 2009-10ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/texlive-doc/latex/expl3/../../../texlive-latex3/latex/expl3/expl3.pdf