Where shall I put my includes for my PHP

I have added the following to my page:

[php]
echo $directory->listCompanies("category_name");
[/php]

I need to include $directory and set a class but I don’t want to do it in the content of the page. I want to add that to a central location, and the plugin be able to recognize the $directory class. Any ideas where I can put that PHP?

https://www.ads-software.com/plugins/allow-php-in-posts-and-pages/