How to give access to custom created PHP pages inside Joomla 3.4.1 folder

Question

My Joomla is installed inside sub folder called "arc" of my main website (http://www.example.com/arc).

I added a custom PHP page called reg_process.php inside the folder named "registration" under Joomla (arc) folder. But I'm having Forbidden access error when I access http://www.example.com/arc/registration/reg_process.php

Please help me.

Thank you,