How to make a non-Drupal page and where to place it? I need to create a page (it's receipt) which is not drupal-page. How it should work:


User clicks the link in "User Menu" or in "User Profile"
This link is made from link to custom page itself and user's $POST parameters (name and address fields, for example).
This page consists of HTML tags, CCS styles and PHP $POST-parameters and finally creates a PDF (to print).


I know how to make modules and use Hooks (I made custom registration), and I can use Drupal database (normal and fields entries). But how I should realize this task? And where I should place my custom page's file?
You need to create a custom module and implement hook_menu() for you custom page.
Here you get details about hook_menu "https://api.drupal.org/api/drupal/modules!system!system.api.php/function/hook_menu/7".

To get this link on user menu tab use type as
 'type' => MENU_DEFAULT_LOCAL_TASK
And write your page code by calling a function
'page callback' => 'user_details',

create user_details function and write code for custom page.