Question 1

Which pages do I type — the ones to keep or the ones to remove?

Accepted Answer

The ones to remove. Everything you don't list is kept. If you would rather describe what to keep, use the split tool instead — it does the opposite.

Question 2

What if I delete every page?

Accepted Answer

You get an error instead of an empty file. A PDF with no pages is invalid and most readers refuse to open it, so the tool stops you rather than handing you something broken.

Question 3

Are the remaining pages changed at all?

Accepted Answer

No. They are copied across unchanged, keeping their text layer, images and page size. Bookmarks or links that pointed at a deleted page will no longer resolve, which is unavoidable once the target is gone.