Just tried an AutoCAD 2000 .dxf (From AutoCAD 2018) and it wouldn't open it. I've spent a fair amount of time trying to get files that work with it, and have not had any lock.
If it can't read .dxf files from AutoCAD, which defines the .dxf format, then it's useless to me.
As it is, it only supports a non standard (incorrect) format of .dxf file.