It´s a plugin to be used with Cinema 4D
The instructions below I copy from Graphisoft website.
The link is :
http://www.graphisoft.com/products/archicad/addons/cinema_4d/cinema4d_download.html
ACMerge plugin for Cinema 4D R11
Optional functionality: Download and install the ACMerge plugin for Cinema 4D R11. This plugin extends the data exchange functionality with scene update: It updates a file already opened in Cinema 4D with a newer version of the exported file without loosing modifications that had already been applied.
Install notes:
Make sure your Cinema 4D is updated to version R11.027 or newer
Download the ACMerge plugin
In Cinema 4D, select the Help menu/Manual Installation... command to locate and load the plugin
Important: for Cinema 4D R11.5 the ACMerge plugin is part of the package.
Note: The ACMerge plugin for Cinema 4D R11 is developed and maintained by Maxon. For support, please contact Maxon Tech Support