If you’re working in a word-processing document, you can set the top, bottom, left, and right document margins. In a page layout document, you set margins for headers and footers. Your settings apply to the whole document.
Tap 
, then tap Document Setup.
Drag the double arrows on the top, bottom, and sides of the document body to set the margins.
For documents that use facing pages, you see two pages in Document Setup. The margins of both pages change as you drag the arrows.
Tap Done in the top-left corner to close Document Setup.