Missing Mathematical Symbols
Kindly see linked PDF ( also attached ) with the missing symbols problem. pdffonts
shows that all fonts are embedded. It may be pertinent to note that these symbols are shown in the PDF viewer shipped with modern browsers (Firefox and Chrome) on the same platform that libpoppler is being used. Compare for example rendering of page 27 using Evince or XPDF with the same page rendered in the browser PDF viewer.
PS: I am aware this issue may duplicate #1253 but I am re-filing it just in case. Kindly feel free to close if you think this is a duplicate. I have also put a comment in the original issue. The problem is not specific to Okular and happens with all PDF readers using libpoppler.