ObjectARX applications can use custom objects.

If these applications or the corresponding object activators (Object Enabler) are not available when opening such a file, Autodesk® AutoCAD® converts these objects "proxy objects" (or zombie).

When you're sure you do not need these objects can be deleted to reduce the file. To do this, run the command KILLZOMBIES and choose the applications for which you want to delete the proxy objects.

A LISP function named gc-killallzombies removes all the proxy objects and proxy entities found in the drawing.
(gc-killallzombies) returns a list of the quantities of objects found and erased of type:
(("ProxyEntity" found erased) ("ProxyObject" found erased))

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin. You may need to restart the Autodesk product to activate the app/plug-in. To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, click Control Panel > Programs > Programs and Features (Windows 7/8.1/10/11) and uninstall as you would any other application from your system.