“That’s how the FBI can trace threatening letters as well.”
Exactly. If you think you’re sending a printed anonymous document, you’re not. Rush had a segment on this many years ago, and I never forgot it.
This is true if you are using a personal printer, an Epson or H.P. Pretty sure this would not apply to a printing company unless they are doing some of the things that the Treasury Department does with printing currency. (Who knows?)