For documents like PDFs, there’s no way to position canonical tags while in the webpage header mainly because there is not any web page segment. In these types of situations, you’ll ought to use HTTP headers to set canonicals. Rel=canonical must only appear within the of the doc. A canonical https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-google-rich-snippets-json-ld-opengraph-twitter-tags-schemaorg.html