Grab https://podatki.gov.si/dataset/615a4e72-da2c-47d3-9246-62c60155ba1b/resource/8c895c90-313a-4610-beae-0aad6f6ea66b/download/evidencadolgoronihfinannihnalobjan24.xps and run okular on it. To compare, run MuPDF on it. Observe that in Okular, all the text is italics or slanted, whereas it should be upright. Parts of it should be bold.
Of course, we assume here than MuPDF does a more precise job on the file than Okular.
In the attachment, you find the original file and its rendering by the two viewers: MuPDF on the left and Okular on the right.