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First, click View > Normal. This gives you a reduced-functionality view of
the document. Now you can go to Tools > Options > General and uncheck the
first box, Background repagination.

The Normal view has some characteristics you might not care for. It can't
show any floating objects (pictures, graphs, text boxes, tables), only
in-line pictures and tables. It doesn't show headers and footers, or page
borders, or backgrounds. Basically, it's great for throwing huge amounts of
text into the document. When you're ready to format the pages, then you
switch into Page Layout view.

As soon as you go into Page Layout view (either from the View menu or by
opening a header or footer), Word automatically turns on background
pagination. It has to, because that's the only way it can figure out what
goes on which page.