In Ubuntu 14.04, 16.04 and 16.10 open the terminal and type:

sudo apt-get install python-pypdf  

Upstream Debian repositories no longer have the python-pypdf package in the latest stable version of Debian. In Ubuntu 17.04 (and later), open the terminal and type:

sudo apt install python-pypdf2 # Pure-Python library built as a PDF toolkit (Python 2) 

Ok, from your comments, you are not using Ubuntu, but Parrot Security OS.

Below command shows where is python-pypdf in my Ubuntu 16.04

$ apt show python-pypdf
Package: python-pypdf
Version: 1:1.13-3
Priority: optional
Section: universe/python

For Ubuntu, below command can add/enable some additional repository which has community maintained free software including python-pypdf

$ sudo apt-add-repository universe
$ sudo apt update

I think you should search/ask this question in Parrot Community.

You can simply install it using pip or pip3 if you're using Python3.
The command is:

pip install pyPdf  # use pip3 with Python3