Applications shows a brand on real things like cards, signs and screens. The mockups are good at that, but plenty of real work doesn't fit one, like a printed piece you photographed or a layout you exported flat.
Now the Applications form has a Your images grid. Upload your pictures, give each one a label if you want, and they appear on the page after the mockups, shown whole on the same mat so nothing gets cropped.
It takes images only. A PDF still belongs in Assets as a download, where people can save it. The ask behind this one came in the day before it shipped, from a studio that needed its flat graphics on the page.