For each section, verify that page numbering is correctly set to
"Continue from previous section" (in the Page Number Format dialog
box). If the document has continuous sections that occupy less than a
page, you can insert temporary page breaks to access the header/footer
area for those sections.

If the problem still remains, the document might be corrupt. Try
saving as HTML, which sometimes fixes corruption.

Or, as you've already tried, copy the contents minus the final
paragraph mark to a new document. Note that for a multi-section
document, you would have to either delete section breaks or copy on a
section-by-section basis (omitting each section break). In either
case, you'll have to recreate section formatting (headers, footers,
margins, etc) in the new document.

For more, see:

How can I recover a corrupt document or template – and why did it
become corrupt?
http://word.mvps.org/faqs/apperrors/CorruptDoc.htm