The F12.dll file is typically associated with the Developer Tools in Internet Explorer and Microsoft Edge. The "F12" label is a reference to the function key used to open Developer Tools in these browsers. Developer Tools offer a variety of utilities for debugging, profiling, and understanding the behavior of web pages. This includes utilities for inspecting HTML, CSS, and JavaScript, as well as monitoring network activity, and other tasks useful for web development and debugging.
The F12.dll library contains the code that powers these Developer Tools. This means that when you open Developer Tools by pressing the F12 key (or by using the menu), the functions from this DLL are loaded to provide the various capabilities of the toolset.