I am using headers and footers in my document. I noticed that Word systematically adds an indent on the first line of every page, as though it were the beginning of a paragraph, and that indent is non-negotiable : if I try delete in that region the first words of the page move on to the preceding page.

I presume that this is not default behavior, and that I did something wrong somewhere. My guess is that the ident is there to add some spacing between the page number in the header and the first words of the page.