Revit supports export to several computer-aided design (CAD) formats.
DWG (drawing) format is supported by AutoCAD® and other CAD applications. 
DXF (data transfer) is an open format supported by many CAD applications. A DXF file is a text file that describes a 2D drawing. The text is not encoded or compressed, so DXF files are generally large. If you use DXF for 3D drawings, you may need to perform some cleanup to make the drawings display correctly. 
DGN is the file format supported by MicroStation of Bentley Systems, Inc. 
SAT is the format for ACIS, a solid modeling technology that is supported by many CAD applications.
If you use one of the export tools for a 3D view, Revit exports the actual 3D model, not a 2D representation of the model. To export a 2D representation of the 3D model, add the 3D view to a sheet and export the sheet view. You can then open a 2D version of the view in AutoCAD.
Before exporting a Revit model, consider these best practices:
- Reduce the amount of model geometry to be exported. See About Limiting Model Geometry Before Exporting.
- Create or modify layer mapping to ensure that all the information stored in Revit categories and subcategories will be exported to the proper CAD layers (or levels, if exporting to DGN). See About Layer Mapping for Export.
- Adjust the view scale to control the precision/performance ratio.
When you export to 2D DWG or DXF, you export a scaled 2D view of the model. The view scale you apply determines whether the resulting view is exported for precision or for performance. For example, if your model contains 2 lines that are 1/4" apart and the view scale is 100, the lines will be considered to be within tolerance, and the exported DWG will contain a single line (exported for performance). If the view scale is 20, the exported DWG will contain separate lines (exported for precision).