I am new to web development so I do not know what exactly causes the problem: apache2 or ubuntu or something else. Yesterday I followed this tutorial ([https://www.digitalocean.com/community/tutorials/how-to-deploy-a-flask-application-on-an-ubuntu-vps) and deployed my fist app online(Ubuntu 14.04 and apache2). It is written in Flask/Python. My app writes some data to a text file which is used later for generation of a pdf file which is displayed to the user using PDF.js extension. Unfortunately, a pdf is not displayed because either a text file was not generated or pdf is blocked from displaying. Everything works great on my local server. So, I am wondering how to give permission for writing a file and displaying a pdf. Any suggestions are highly appreciated!