The section break (not page break) contains your document's formatting.
It is a "next page" section break.
It is followed by more than 50 empty paragraphs formatted at font size 1 pt.
This happened, apparently, because you selected a portion of your document and changed the margins for that selection. That inserted a required next-page section break. Since page margins cannot be changed in the middle of a page, a new page is required.
Margins and Indents in Word
The way to fix this is to, before the section break, record a macro in which you visit each of the page layout dialogs, the margin dialog, the page size dialog, and the orientation dialog. OK out of each dialog box. Then move your insertion point beyond the section break and run the macro you just recorded.
Insert a continuous section break before the next-page section break to preserve headers and footers.
Then select and delete the next-page section break.
See the attached revision.
Delete a Next-Page Section Break that Word won't delete