If you have BabaCAD freeware version (all BabaCAD versions in years 2012-2017), you can open only .dwg drawings <R2007 and dxf files.
If you need to work with all .dwg drawings (R12,R13,R2000,R2004,R2007,R2010,R2013,and now R2018), you have to purchase BabaCAD Home or Enterprise Edition (BabaCAD HE/EE 2018).