A PDF often carries pages you don't need: blank pages from a scanner, a cover sheet, an outdated annex, a confidential section you shouldn't forward. Removing them takes seconds.
You download a new PDF; the file on your device is not touched. Open the original again and start over.
Remove pages gives you everything except the pages you mark. If it is easier to say which pages you want to keep, use Split PDF with Pick pages instead.
Do it now: Remove Pages