You can import additional drawing layouts into your sheet set using the Sheet Set Manager (SSM).
The term import, however, may not be what you expect from your experience with importing other data in AutoCAD. Remember that the sheets in the SSM sheet list are nothing more than shortcuts or pointers to layouts in drawings.
When you “Import Layouts as Sheets” what you’re really doing is simply creating a new pointer to an existing drawing.
This post by Autodesk's Heidi Hewett a frequent contributor to the offical
You can download the entire free Mastering AutoCAD Sheets Set ebook