I have a text-box containing a hyperlink to the Falstad circuit simulator with a simulation of that part of the circuit. I want the text-box to be on the sheet, close to what’s being simulated because there are usually several, and it should not print when made into a PDF or printed.
You can add a datasheet link to any schematic symbol. And it does not have to be to a .PDF file. It can also be an image, or an URI KiCad just throws it to your OS, and that can do whatever with it that it likes. Datasheet links are normally mapped under the d key, and quite a lot of the default symbols have a datasheet link attached, so you can look at the syntax on anyone of them. I personally use datasheet links with a custom environment variable to point to locally stored datasheets.
I think I even used a datasheet link to another KiCad project once, and when activated, my OS just opened that other KiCad project in a new KiCad instance