/usr/share/doc/libopenthreads-dev/changelog.Debian.gz is in libopenthreads-dev 3.2.3+dfsg1-2ubuntu8.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libopenthreads-dev/../libopenthreads20/changelog.Debian.gz