You tried going to https://kouzelnickysvet.cz/wp-content/plugins/pdf-poster/pdfjs/web/viewer.php?file=https://kouzelnickysvet.cz/wp-content/uploads/2020/01/Kniha-Pravidel-1.pdf&download=true&print=false&openfile=false
, which doesn't exist. You can try navigate or search.