How to include an external PHP script? I have PHP file and I need to include that PHP file in static page. Where is best place to store that PHP file so I can include it in a static page.
If that's your code, transform it into Drupal custom module. If you want use PHP API delivered by external service - transform it into library (move code into  sites/all/libraries/yourLibrary) and write custom module which loads files on demand (with Libraries API).