Why this exists
Most converters are built for pictures. That is a different job from building a file that a laser, a router or a cutter will run, and the difference only shows up after the material is scrap. A watermark in a DXF is extra cut paths. A file with no declared units comes out 25.4 times too big. An outer boundary cut before its holes drops the part through the slats. None of those are rendering problems, so a converter aimed at pictures has no reason to solve them.
How it works
Everything runs in the browser. Your file is read by the page and never uploaded, which is why conversion is unlimited and free, why it works on a drawing you are contractually forbidden to send anywhere, and why it keeps working with the connection off once the page has loaded. Paid plans cover the machine formats and the work that genuinely needs a server.
What we will not do
We will not put a watermark in a file that drives a machine, at any tier, because somebody would run it. We will not claim a tool does something it does not: the format matrix marks what is built and what is planned, and the planned ones say so on their own pages rather than failing quietly.