Most users are aware that AutoCAD uses "Support Paths" which identify the locations where both dependent AutoCAD files and any custom files (ie. lisp addons) reside. Since AutoCAD defines multiple support paths and the fact that you can include your own additional paths, locating a file within one of these locations can be a tedious process; especially since later versions of AutoCAD point to locations outside of the installation directory.
That being said, using a single line of lisp code at the command line in AutoCAD makes locating these files a breeze. In lisp, the FINDFILE function searches all of your support paths for the file that you specify. Therefore, as an example, if we wanted to search for the "ACAD.PAT" file within the support paths we would simply enter the following at the AutoCAD command prompt and hit enter:
Looking at the image we can see the exact path to this file (click on image to see it enlarged).