Does not open any of my .dwg files

When I drag known .dwg files into the DFX Viewer it tells me they do not appear to be .dwg files???? The files open fine in AutoCAD on PCs at work, and I need to view these files at home on my iMac. Unless I find out what’s wrong, this app is worth nothing to me.
Thumbs Down!

Virgil1950 about DXF View - View DXF™ & DWG™