Cooper utilizes cooperative mutation to test the binding code of scripting languages to find memory-safe issues. Cooperative mutation simultaneously modifies the script code and the related document objects to explore various code paths of the binding code. To support cooperative mutation, the authors infer the relationship between script code and document objects to guide the two-dimensional mutation. They applied their tool Cooper on three popular commercial PDF tools, Adobe Acrobat, Foxit Reader, and Microsoft Word. Cooper detected 134 previously unknown bugs, which resulted in 33 CVE entries and 22K bug bounties.