How to include WordPress functions in custom .php file?

Question

How can I include WordPress functions in a custom .php file?

In detail: I have a directory under my theme (Constructor) named reports. These contain

Answer 1

External files can easily access the WordPress functions. You just need to include the file wp-load.php in your external file. The wp-load.php file is located in root of your WordPress installation. Example: Suppose your file is test.php located at root directory of WordPress installation.

Source: How to access WordPress functions in external file