CADDManager on February 3rd, 2010
You can attach a DWF, DWFx, DGN, or PDF file as an underlay to a drawing file.
You reference and place underlay files in drawing files the same as you do raster image files so they are not actually part of the drawing file. Like raster files, the underlay is linked to the drawing file through [...]

Continue reading about Attaching PDF Files in AutoCAD 2010