try a AECTOACAD command (look it up if needed) It normaly takes 3d CAD files and flattens them just fine for our company.
---suffix = 1
(it will create a NEW CAD file where ever the current file was located. so just close out of the current file and go to the same folder it was in and you will see a new file with a "1" after it, open it and it should all be flat)
fyi make sure you are not trying to flatten a block, must BURST it forst.
hope this works for ya.
The FLATSHOT command is what your looking for, I believe. You have the option to keep hidden lines and put them on a different color and linetype or to leave them off and produce a realistic looking plan view.
If your using MEP objects they won't flatshot (I believe it's only 3D solids that are captured) so you will have to be in an isometric view and use the CONVERTTO3DSOLIDS command.
ok so im new to autocad. im using a mac. please help. i have a 3d line drawing of a topo. and im trying to flatten it. i have tried flatshot but does not seem to help. there are not surfaces just lines. i figured this out when measurements were all messed up. i have have been looking at the file from top view not knowing of the 3d component .. any advice.?