You can open an artifact, click edit, and use the Insert function to add a table, horizontal line, image, another artifact, symbol, or a link. However, you cannot attach something to it a specific artifact. The reason is that whatever you want to attach is supposed to be its own artifact. In a particular instance, I could insert an image to a text artifact, or I could create an artifact of the figure type and link it to its related artifacts (which is my prefered method). I do something similar with regulatory requirements: I add the source document as its own artifact, extract a set of regulatory requirements, and link the requirements back to their source document.

Basically, Rational DOORS Next Generation uses links between artifacts instead of attachments. Links provide traceability, while attachments complicate it.

If my leadership asked me to download all the attachments, that would provide an opportunity for requirements elicitation. what do they mean by an attachment? Can they define what they need using other terms? Can they provide an example? Has anyone else done something similar? Do they have a job guide or SOP for the process?