Customize document content before it is indexed by SearchWP

searchwp-customizations.php

<?php

// Customize document content before it is indexed by SearchWP.
add_filter( 'searchwp\document\content', function( $content, $the_post ) {
  if ( 18 === $the_post->ID ) {
    // Add 'coffee' to the document content so it can be searched.
    $content .= ' coffee';
  }
  
  return $content;
}, 10, 2 );