I have many items in my library that include different types of supplementary files, including PDF files, but also movies, code, databases, ...
With the current interface, it seems that it is not possible to see any of these supplementary files child items from the Zotero PDF viewer?

From what I have tested, the only way to see all the child items is to go back to the main library. But if I have several PDF files open, I don't see any way to go back to the item in the library?

The approach to do this in Mendeley is to show the "Files" inside the right-hand side info pane, together with the metadata of the item. Is there any technical limitation to do the same in Zotero, or is it a design decision driven by other considerations?

Listing the supplementary files child items together with the notes child items could work, but I would really prefer to be able to see all child items related to a PDF file directly from the default view offered when opening the Zotero PDF viewer.