/usr/share/doc/libfftw3-3/changelog.Debian.gz is in libfftw3-3 3.3.3-7ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libfftw3-3/../libfftw3-double3/changelog.Debian.gz
/usr/share/doc/libfftw3-3/../libfftw3-double3/changelog.Debian.gz