hi,i have an stl file i want to decode it so can u tell me how can i decoded that file please reply asap.

What program other than AutoCAD do you have available to you?Where did you get the .stl file from?

Try using MESHLAB.  It can import .stl files and export .dxf files.http://meshlab.sourceforge.net/

You can try the STL to DXF online converter:http://www.cadforum.cz/catalog_en/stl2dwg.asp

Some of those so-called converter programs really make one wish they hadn't been used at all.  The conversions tend to be of very poor quality.