If you are using Adobe Acrobat Reader to view the PDF, the most reliable fix is to install the official, free Asian Language Font Pack provided directly by Adobe.

Search for the for your specific operating system (Windows or Mac).

Instead of searching for a download, you should use the following proven methods to fix the PDF rendering: 1. Re-Export/Print to PDF (The Easiest Fix)

Created by Adobe, CID-keyed fonts can store a huge number of glyphs, making them ideal for complex writing systems like Chinese, Japanese, and Korean (CJK). However, they aren't commonly installed on personal computers.

Sometimes Adobe Reader struggles with specific CID mappings, while other viewers do not.