custom files with permalinks from theme folder

Hi.

I can call custom files (php or html files not associated with WordPress in any way, like a custom made image viewer) using the permalink structure, for example, show.php can be called in my host via https://www.nn45.com/main/show .

But I need to put those files on the absolute path of the WP installation, and I want to put those files in the theme folder (wp-content/themes/theme-folder), and call those files in the same way, I mean, can put the show.php file into my wp-content/themes/theme-folder, an call it in the same way like before (https://www.nn45.com/main/show). Someone knows a way to do this?

Thanks.