Seiss,
You can X-REF in the DWG file. It will give you all of the, layers, line types etc, btw the layers of an X-refed DWG are defined by the name of the DWG and a vertical line followed by the actual layer name,
of the DWG but once you have finished with it, you can do a simple detach.
When detaching the DWG, you will be given an option to keep or to delete the attributes of the DWG file.
You can find the X-REF manager under the Modules and X-Refs menu, which can be found under the file menu of ArchiCAD.
HTH
Cheers.
Ben