"Staple" or "group" pages within a PDF.
"Staple" or group pages to keep specific pages in a multipage PDF together. User is warned if trying to edit the stapled pages but can override if required. Selecting one page in a stapled group would select all pages of the group for moving, extracting, deleting, etc., with warnings. Access to act on specific group page page could be enabled with alt, multiple pages in the sub group with alt-shift or ctrl-shift. Prompted by: similar subdocuments were combined into a larger PDF, but the naming of the subdocuments may make it unclear where new additions should be placed.