/usr/lib/libplplotf77d.so.9 is in libplplot-fortran9 5.9.9-2ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libplplotf77d.so.9.1.1
/usr/lib/libplplotf77d.so.9.1.1