How to add page numbers to a PDF
Open Add page numbers, add your PDF, choose the position and style, press Start and download. Skip the first page if you have a cover.
Pick a position
Bottom center suits most reports. Choose the outer corner for anything printed double-sided, so numbers don't vanish into the binding.
Keep the cover clean
Skip the first page, and leave the first number at 1 so the page after the cover shows 1. If you'd rather have it show 2, start at 2.
Do this step last
Number the file after you've merged, reordered and deleted pages. Otherwise the numbers move with the pages and end up out of sequence.