Drawing Interchange File Formats
ASCII DXF File Format
General File Structure
DXF File Structure

The overall organization of a DXF file is as follows:

APPID (application identification table) BLOCK_RECORD (block reference table) DIMSTYLE (dimension style table) LAYER (layer table) LTYPE (linetype table) STYLE (text style table) UCS (User Coordinate System table) VIEW (view table) VPORT (viewport configuration table) If you use the Entities option of the DXFOUT command, the resulting DXF file contains only the ENTITIES section and the EOF marker. The ENTITIES section contains only the objects you select for output. If you select an insert entity, the corresponding block definition is not included in the output file.