Just wanted to share a tip if your customer or yourself is using a marketing automation tool such as Autopilothq, (awesome tool btw, kinda of the webflow of marketing automation).
So, say you want to add a hidden field to capture the resource name that has been downloaded on a challenged piece of content. I first tried the solution posted on this forum (type="hidden") but this was not detected by the automatic form capture feature Autopilothq's platform offers.
In the end, I used the style="display:none" and it worked like a charm.
I don't know if this will help someone but thought I would share either way :-).