Basic edit thing for experts

1 which options can edit pdfs? archtiect creator or all of them
2 can they edit pdfs you downloaded i guess so like docs and other things
3 there's an outline on right side in any pdf readers like chrome pdf, you click on icon for the outline/toc
4 wanna know how to edit that outline
5 also wanna konw what tools can auto-generated an outline if pdf doesnt have one

what tools/options on web can auto-generated an outline if pdf doesnt have one - that's goal

cos want to edit an outline into pdfs without one