/usr/share/doc/libgnuradio-fcd3.7.2.1/changelog.Debian.gz is in libgnuradio-fcd3.7.2.1 3.7.2.1-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgnuradio-fcd3.7.2.1/../libgnuradio-pmt3.7.2.1/changelog.Debian.gz