Adding a .php extension to pages does not work

I am trying to add .php extensions to all pages.

I chose "custom structure" under settings > Permalinks and changed it to look like this: /%postname%.php The blog posts are working but my page url's are still without .php

- I just started developing this website, so there should be no conflicts.
- I tried changing the theme to default and still does not work.

What am I doing wrong?