/usr/lib/libgtkhtml-4.0.so.0 is in libgtkhtml-4.0-0 4.6.6-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libgtkhtml-4.0.so.0.0.0
/usr/lib/libgtkhtml-4.0.so.0.0.0