/usr/share/doc/apt-cacher-ng/html/ is in apt-cacher-ng 0.9.1-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/doc/apt-cacher-ng/html/Intro.html
/usr/share/doc/apt-cacher-ng/html/bugs.html
/usr/share/doc/apt-cacher-ng/html/config-serv.html
/usr/share/doc/apt-cacher-ng/html/config-servquick.html
/usr/share/doc/apt-cacher-ng/html/cont.html
/usr/share/doc/apt-cacher-ng/html/distinstructions.html
/usr/share/doc/apt-cacher-ng/html/howtos.html
/usr/share/doc/apt-cacher-ng/html/index.html
/usr/share/doc/apt-cacher-ng/html/maint.html
/usr/share/doc/apt-cacher-ng/html/secure.html
/usr/share/doc/apt-cacher-ng/html/troublefaq.html
/usr/share/doc/apt-cacher-ng/html/usage.html