What is a WLL file and how can it be used for persistence in Microsoft Word?

A WLL file is simply a renamed DLL that is placed in the Word Startup folder (`%APPDATA%\Microsoft\Word\Startup`). When Word launches, it automatically loads any WLL files in that folder, executing their code. An attacker can create a DLL that runs a payload (e.g., calc.exe or a reverse shell) in its `DLL_PROCESS_ATTACH` handler, achieving persistence every time Word starts. For more details, see Use Office to maintain persistence.