/usr/share/doc/libgtkhtml-4.0-dbg/changelog.Debian.gz is in libgtkhtml-4.0-dbg 4.6.6-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtkhtml-4.0-dbg/../libgtkhtml-4.0-0/changelog.Debian.gz