When you've got non-HTML pages on your internet site, which include PDFs or spreadsheets, you won’t be capable to employ hreflang from the of your HTML since it doesn’t exist.  For those who’re syndicating or republishing material on other web-sites, this is another time and energy to use canonical tags. https://www.presta-addons-modules.com/en/opencart-seo-automatic-google-rich-snippets-json-ld-integration-opengraph-twitter-tags-schemaorg.html