theyre microscopic. theyre typically used to track printers doing illegal stuff (e.g counterfeiting) and leak tracking if someone when to scan some document and post it somewhere it shouldnt be. Of course, this is antithetical to privacy. The yellow dots are microscopic throughout the page.

https://en.wikipedia.org/wiki/Printer_tracking_dots

You can’t. They’re microscopic.

It's only common on color laser printers.