How to remove or keep PDF pages
To drop a few pages, use Delete PDF pages. To keep a few, use Extract PDF pages.
Which is quicker?
Count what's quicker to pick. Removing 3 pages of 50 suits Delete. Keeping 3 of 50 suits Extract. In both, you can tap the pages in the thumbnails instead of typing.
Typing page numbers
Use commas and dashes: 1, 3, 10-12. A dash with no end number means to the last page.