Could be one or other of two things (or both of them): The doc is 'Read Only' and/or the page size is set to 'Letter' and you are using A4.
First make a copy of the document (to play with). rightclick the copy file and click on 'Properties', untick the 'Read Only'
Open your copy of the document and click on: File | Page Setup | and 'Paper' tab and choose A4 from combo drop down list.
Click on 'Layout' tab and alter Headers and Footers from edge of paper. (this is the measurement that leaves a gap (blank part) before the Header starts and leaves a gap (blank part) to the edge of paper after the Footer has finished.