Sometimes, you may find that when open dwg file, and it will pop up a message telling you that the drawing is produced by an educational product, not for commercial use. When you plot, you will have the edu stamp there.

The reason is that the drawing has been saved in EDU or we can say academic version before. Actually, ZWCAD 2018 SP2 to 2020 SP1 doesn't pop up the education message, and plot without any edu stamp, and when save the file, it will remove the edu stamp, but before and after, which means the version 2018SP1 or previous versions and 2020SP2 or afterward versions, we will check the stamp, and apply to plot, and will not remove the edu stamp when save.

You can check with the customer, and they can turn off EDUCHECK to avoid the message and plot stamp in ZWCAD, but the edu stamp is still inside the file.

You can also try to save the file in ZWCAD previous version, or use the free tool DWG Converter (can find it in ET) to remove the EDU stamp.