Luke is right in saying that DXF files don’t typically have standardized units assigned to them.

Exactly right! In that vein, there are those that also use AutoCAD online.

The most common is from the Open   – they have support for native apps (macOS, Windows, Linux) and WebApps.

If you’re looking for an open-source alternative you could search GitHub for a DXF Viewer. For example ‘Simple DXF Viewer by Yangosoft’ .  I have no idea if that’s any good. It’s just the first I found.

https://designsdxf.com/