when opening a pdf document with Acrobat Reader DC I have trouble displaying strange characters. This problem does not occur in other browsers or programs. Installing the latest updates and setting the language as it is on system did not help.
It appears that the font information is not embedded in the pdf file and you don not have the exact font on your system. Reader is trying to substitute with a different font but that isn't working. Not much to do about that accept to contact the creator of the pdf and ask them to embed the fonts.
Other pdf viewers tend to not care about pdf's sticking to certain specifications like Adobe does. Many of them also do a better job at substituting fonts.