AutoCAD 2012 improves the ability to highlight and select externally referenced files. If you pass the cursor over the edge of an attached image, DWFTM, or PDF file, a selection preview frame is displayed, even when frames are turned off.
Similarly, passing the cursor over geometry inside an attached DWF, PDF, DGN, or DWG file displays a selection preview frame. You can select the frame for any of the attached reference files to display a frame boundary, with the ability to grip-edit a clipped boundary frame.
Interaction with the External References manager is enhanced to automatically display the frame when you select a reference file from the list.
To support the frame selection behavior, a new FRAMESELECTION system variable is included in AutoCAD 2012.