hope someone can help im trying to open dxf files   as need to convert them into a cad version that i can open with artcam pro 9.1    but i have tried 2 auto cads and neither will open the dxf file  is there a way of finding which version created the document 

There are many DXF files which are not formatted properly. But a DXF file (text-based) should start with something like this:  0SECTION  2HEADER  9$ACADVER  1AC1009and the "AC1009" (or similar) will match the AutoCAD version - see https://www.cadforum.cz/en/qaID.asp?tip=868But any newer version of AutoCAD will open properly formatted DXF and DWG files from an older version.

Thanks for your reply. I have looked at file using notepade and it all looks similar to what you posted but no matter what cad I try it fails errors saying drawing not found and closes

Well, the Autodesk DXF format specification is quite wide - if a DXF file does not conform with that specification, it probably won't be readable for AutoCAD.