/usr/lib/x86_64-linux-gnu/libplplotadad.so.1 is in libplplot-ada1 5.10.0+dfsg2-0.1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libplplotadad.so.1.0.0
/usr/lib/x86_64-linux-gnu/libplplotadad.so.1.0.0