I can’t find out how to insert the page number on all pages.
First you have to find out whether each of your pages is based on the same page style. If yes, so insert a footer (menu Insert) and after that click with mouse into the footer and hit the Tab key. So the cursor will show in the middle of the footer. Click again menu Insert and there you find page number. If you haven’t changed the position of cursor the page number will appear as wanted…
If your document is based on several page styles you have to proceed the same way for each of them. You may note the page style in the status line (cursor must be located in this specific page).