If you are using Adobe Reader, ensure that the Asian language packs are installed. Go to the Adobe website to download the "Adobe Acrobat Reader Font Pack" to handle CJK characters.
If you are trying to view a document in a web browser or a third-party app and it looks corrupted, you can re-embed standard system fonts to overwrite the missing reference. cidfont f1normal font free download link
"CIDFont F1Normal" is essentially the program saying, "I am displaying the Regular weight of the first font used in this PDF, encoded in CID format." If you are using Adobe Reader, ensure that