With hieroglyphic languages (Chinese, Japanese, Korean) PDF export with incorrect parameters may produce □ character instead of recognized hieroglyphs.
To prevent any distortions of hieroglyphic characters, you must specify a font which includes hieroglyphs, e.g. Arial Unicode MS, SimSun. You can do this with the help of the ISynthesisParamsForDocument::AddRecognizedTextFontName method. A set of suitable fonts can be included to the set of fonts, which are used during document synthesis by default, using the AdjustRecognizedTextFonts property of the SynthesisParamsForDocument object.