Does my manuscript upload to your server when watermarking?

No. The ARC Watermarker reads your file and stamps each personalized copy entirely in your browser — your manuscript never leaves your computer. You download a ZIP of the stamped copies and send them yourself.

The one exception is ARC Delivery: when you choose to have us email the copies to your reviewers, those files do pass through our system to be sent (and are deleted after the links expire, within 30 days). If you use the Watermarker and send the files yourself, nothing uploads at all. See What is the difference between ARC Watermarking and ARC Delivery?