/usr/lib/x86_64-linux-gnu/libptexenc.so is in libptexenc-dev 2015.20160222.37495-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libptexenc.so.1.3.3
/usr/lib/x86_64-linux-gnu/libptexenc.so.1.3.3