How to save the opened dxf file as dxf by the one command

Hello

I would like to save my opened dxf drawing again as dxf with one click by custom button.

I was trying the next code

^C^Cdxfout;;y;v;2004;16;; 

It returns the message "Can't open file", it seems like it does the save only when initial file is dwg.

The goal I wish I click a custom button and will save my opened dxf drawing back to dxf in 2004 format.

Please advise how to do it.

Best regards,

Orest Yavtushenko