I've created same topic in Civil 3D, but I think here I'll an answer faster.
I have GeoPDF that I can't attach properly to drawing in Civil 3D.
So with Global Mapper I exported it to geo-referenced ECW.
I checked ECW in Global Mapper and ArcMap, everything just fine.
However when I did mapiinsert in Civil 3D, image appeared with shifted coordinates.
The original coordinate system of PDF and ECW is BC/Albers and coordinate grid is Lat/ Longs.
I've uploaded ECW, if somebody could try it.
This is a picture from Civil 3D with Lat Long grid above the image.
In my Map2006 CRS list, there is no BC Albers, so I created it by scratch basing on EPSG:3005 parameters (command _ADEDEFCRDSYS).
If I load your .ECW in this brand new CRS, and I draw a draft yellow line on the West coast, it fits exactly on Google Earth - check my .ZIP one, unpacking the content in the .ECW folder.
Now you should try to attach my DWG into a LL84 empty drawing (EPSG:4326) by means of _ADEDRAWINGS, then perform a draw query to check the conversion.