For a Joomla site, we scrape the HTML output from the Joomla installation. Then - if you order the WordPress conversion - we convert the HTML pages into a WordPress installation. This does come with some limitations, which you can read about on https://www.waybackmachinedownloader.com/en/wordpress-conversion/
The same process is applicable to sites built with CMS platforms such as Drupal, Shopify and Magento. Please note that due to the limitations as described on the URL above, a site with a lot of custom backend code - such as Magento or Shopify - won't give good results. Ecommerce website will look the same as on archive.org, but it won't function the same because many objects rely heavily on backend code.
In general, our HTML to WordPress conversion is useful for sites with a lot of content, but with little interaction with the visitor. Good examples are magazines, news sites, blogs etc.