Adobe Flash Player was discontinued on December 31, 2020, and blocked Flash content from running in Flash Player effective January 12, 2021. This affected features in Gaaiho Doc and Gaaiho PDF Reader which use Flash components (e.g. preview of "packaged" PDF files).
The version 5.4 ensures the compatibility of PDF files after EOL. Please update to the latest version. For users of Gaaiho PDF 4 or older, please consider a upgrade to the latest version to ensure optimum user experience.