I think Preview may still allow you to edit PDF documents it has open.
In the sidebar, the one that shows the pages, click a page and press the Delete (Backspace) key on the keyboard. If the PDF is editable, the page should be deleted.
At this point, if you wish to preserve the original PDF,
DO NOT choose Save or ⌘S.
If the page was deleted, then go on to select and delete other pages. Repeat as needed. Use Undo as needed.
Then choose "Print..." and look at how many pages will print. It should be less than the total number of pages in the original document. The pages you deleted should not print.
EDIT
I just checked Apple's support documentation, and it confirms that Preview.app can still delete pages from a PDF file in both High Sierra and Mojave.
https://support.apple.com/guide/preview/add-delete-or-move-pdf-pages-prvw11793/10.0/mac/10.13
If you click the
Table of Contents link on that linked page, you'll see a much more extensive list topics for what Preview.app can do.