How can I run a .php file located in my site’s root folder?

I am trying to convert some data from custom post types into custom tables in my WordPress database. I have written a PHP program to do this. It requires that WordPress be loaded so I can use some of WordPress’s database access methods ($wpdb).
I have placed the conversion file in my site’s root directory where index.php resides, but when I try and run it

http://my-site.dev/convert.php/

I get a 404 page not found error. How can I configure WordPress or my server (I’m using Desktop Server locally for development) to run this program?

Installing a plugin had modified my .htaccess file. When I restored to the saved original, I was able to run PHP scripts just fine. Thanks to Denver WordPress Meetup group for suggestions.