Note that headers and footers don't have sections. Sections have headers and footers.
Using the replace function (CTRL+H) to replace ^b with nothing will remove all the section breaks, but try it on a copy of your document or you could quickly discover why the section breaks were included.

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Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com