I have a similar problem. I downloaded this file: https://www.google.com/url?sa=t&source=web&rct=j&url=https://helda.helsinki.fi/bitstream/handle/10138/29945/kieliopp.pdf… and all boldings are gone using adroid app. Concerns both Reader and Digital Editions. File itself is ok, since bold text is actually bold if I open the file with Drive pdf viewer with the same tablet. Reader version 16.1.1, sub-something code for version is 145687. Samsung galaxy tab s2 SM-T810, Android 5.0.2.
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