Load Into Scene
From Nevercenter 3D Modeling Wiki
Default Shortcut: Ctrl + Shift + O
Menu Path: File > Load Into Scene
Description
The Load Into Scene command will load another project into the current workspace, adding its materials and geometry to those of the current project. You can import any of the supported file types.
Many applications have a separate command called Import for files in different formats. To import files into Silo, simply use Open Scene or Load Into Scene, and then select the preferred alternate format.