/usr/share/doc/libthumbnailer-qt-dev/changelog.Debian.gz is in libthumbnailer-qt-dev 2.4+16.04.20160321-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libthumbnailer-qt-dev/../thumbnailer-service/changelog.Debian.gz