Can we use .kml file in autocad?

Yes , To Import it to Autocad

yes, we can use it by importing it to AUTOCAD.

yes , you can

Oui, nous pouvons l'utiliser en l'important à AUTOCAD

yes we can import it using Spatial Manager plugin

If you need to import a KML/KMZ file into Civil 3D or Map 3D, you can do it using a free download from SL-King Spatial Solutions.  

I'm pretty sure the Autodesk supplied Google Earth extension does not provide for import.  If you were to consider third party add-ons, take a look at MapWorks Base which will handle KML files, including projecting them to state plane, etc.  Currently KMZ isn't supported but we could likely add that if needed (it's just a zip file).

If you need to import a KML/KMZ file into Civil 3D or Map 3D, you can do it using a free download from SL-King Spatial Solutions. Be sure to read the readme file because the install does require you to copy some files and edit an existing file.

yes of course we can use it 

yes we can import it, but file being in pdf would better to make the client understand.