As you may have noticed in the previous chapter of this user guide, hovering over an image reveals two additional symbols in addition to “Expand” and “Collapse”:

Magnifying glass: the symbol allows you to inspect a document more closely, opening the selected page in full-screen view. Clicking on the “X” in the top right corner will close the window and bring you back to the default PDF combiner view.
Trash bin: clicking on the symbol will erase all currently selected pages and documents from the combiner tool. Note that you do not permanently delete this content – just remove it from the PDF combiner interface!