A memory corruption issue was addressed with improved state management. This issue is fixed in watchOS 8.5, iOS 15.4 and iPadOS 15.4, macOS Big Sur 11.6.5, macOS Monterey 12.3. Opening a maliciously crafted PDF file may lead to an unexpected application termination or arbitrary code execution.
https://support.apple.com/kb/HT213186
https://support.apple.com/en-us/HT213193
https://support.apple.com/en-us/HT213184