/usr/share/doc/sfftw-dev/changelog.Debian.gz is in sfftw-dev 2.1.5-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/sfftw-dev/../sfftw2/changelog.Debian.gz
/usr/share/doc/sfftw-dev/../sfftw2/changelog.Debian.gz