delete pages

In a word processing document, you cannot remove pages by deleting the thumbnail as that will whack your entire document. You must select the content on the page to be removed and press backspace. I would also have Show invisibles enabled from the View menu in case there are other hidden artifacts on the page that also need removal.

If you have created a Layout format Pages document, then each thumbnail is a page and you and remove a page by deleting its thumbnail.