To Import the Definition of a Component or Folder From an External Drawing (AutoCAD Mechanical Toolset)

Click Structure tabTools panelStructure Catalog. Find
In the External Drawings tab or Favorites tab, select the drawing file that contains the component or folder you want to import the definition of.
From the Mechanical Structure panel in the Details section, right-click the component you want to import. A menu is displayed.
Select Import Definition, the definition of the component is imported and is shown in the Current Drawing tab of the Structure Catalog dialog box.
Note: If the current drawing already contains a component or folder with the same name as the one you are importing, the Rename dialog box is displayed to assist you resolve the conflict.