You can load Revit models (*.rvt) into a project as a group, and you can load Revit family files (*.rfa) into the Family Editor as a group.
If you have existing RVG files (Revit group files with the .rvg extension), you can also load them into a project or family.
To load a project or family file as a group
 Load from Library panel
Load from Library panel
 (Load as Group).
 (Load as Group). When you select attached details, detail elements in the file are loaded as attached detail groups.
The file is loaded as a group, and the group displays in the Project Browser under the Groups branch. You can now place the group in the project or family. See Placing Groups.
To reload a group
If any family types differ between the file you are loading and the host file, the Duplicate Types dialog opens to indicate this.