Where in code to replace content before display of page?

Question

I wish to make a replacement in all pages of a WordPress installation, after the page content has been read from the database and before it is displayed on visitor screen (of course).

Where in the code do I insert the following statement that will make the replacement?

$page = str_replace($target, $replace, $page);

I run an updated WordPress using 2016 child theme. Among others I have a dedicated single.php and a functions.php

Thank you

Answer 1

If you use native editor (and not some PageBuilder that stores data in its way), then you should be able to use the_content filter to do that:

add_filter( 'the_content', 'my_the_content_filter' );
function my_the_content_filter( $content ) {

    $content = str_replace(...);

    return $content;
}

You might put some conditions in there, to check if you modify only pages or only on single page and so on...