$ sudo apt-get update
$ sudo apt-get install libptexenc1 

libptexenc1 is installed in your system.

Make ensure the libptexenc1 package were installed using the commands given below,

$ sudo dpkg-query -l | grep libptexenc1 *

You will get with libptexenc1 package name, version, architecture and description in a table

libptexenc1 package basic information: