ASCII Drawing Interchange file format

Standard ASCII text files used in CAD products such as AutoCAD to store vector data. Uses the extension .DXF.

The basic organization of a AutoCAD DXF file is as follows:

HEADER section - General information about the drawing. Each parameter has a variable name and an associated value.
TABLES section - This section contains definitions of named items.

Linetype (LTYPE) table

Layer table

Text style (STYLE) table

View table

User Coordinate System (UCS) table

Viewport configuration (VPORT) table

BLOCKS section - This section contains Block Definition entities describing the entities comprising each Block in the drawing.
ENTITIES section - This section contains the drawing entities, including any Block References.
END OF FILE

online-documentations of several DXF-versions: