In Civil 3D 2007, as with all 2007 products, we are now able to underlay a DWF file straight into our drawings.
How, you may ask? With the DWFATTACH command. DWF files can also be drag-and-dropped into a drawing.
When a DWF that contains multiple layers is attached all of the data is placed (flatted) onto a single layer.
Attached DWFs can be clipped with the DWFCLIP command. They also have adjustable settings for Contrast, Fade, and Monochrome.
If we xref a file that contains an attached dwf, the dwf will be visible in our file (similar to an attached xref).
DWFFRAME controls the visiblity of the DWF file's Frame and whether or not it will plot.
Just remember DWF's are not 100 percent as accurate as a true vector file (DWG) but they are significantly smaller.