Frequent tipster Leonid Nemirovsky shared with us a tip from one of his coworkers, Aaron Sherry. Aaron often uses Civil 3D, and needs to send those files to clients that only have AutoCAD.
"We use AutoCAD as well as Civil 3D, and we deliver AutoCAD drawings to clients who do not have Civil 3D. If the drawing you're sharing was created in Civil 3D, save it, then use the eTransmit command in Civil 3D. When you extract the drawing from the zip file that was created, it will not have proxy objects created by Civil 3D — meaning it can be opened and worked on in regular AutoCAD. There is a downside: the drawing loses all Civil 3D intelligence in this process."
Notes from Cadalyst Tip Patrol: I love eTransmit. It is the best way to prepare your AutoCAD and AutoCAD vertical files for transfer. When you eTransmit Civil3D files, make sure to use the Exploded AEC Objects option. They will be "dumb lines," but AutoCAD users will be able to use them. Otherwise, they will be proxy objects that your recipients can't do much with.