Since WP Engine deprecated .htaccess support we need to use different methods to redirect old URLs.
They offer a good redirect rule system.
Here’s an solution to redirect the following structure
www.domain.com/wp-content/documents/document-name.pdf
to this new structure
www.domain.com/document/document-name
Source
^/wp-content/documents/(.*?)\.pdf$
Destination
https://www.domain.com/document/$1
