My attempt to upload *.dxf results in:
"File extension ".dxf" does not match the detected MIME type of the file (text/plain)."
I assume that mediawiki believes DXF should be an image format not text/plain.
When I try *.dxf.txt it says:
"Permitted file types: png, gif, jpg, jpeg, dxf, dwg."
I was wrong in my assumption that text files would defaultly be allowed.