/usr/share/man/man1/otr_modify.1.gz is in libotr5-bin 4.0.0-2.2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man1/otr_toolkit.1.gz
/usr/share/man/man1/otr_toolkit.1.gz