Use mirror margins to set up facing pages for double-sided documents, such as books or magazines. The margins of the left page are a mirror image of those on the right page. That is, the inside margins are the same width and the outside margins are the same width.
Click Page Layout > Margins.
Note: To change margin widths, click Custom Margins at the bottom of the Margins gallery. Enter new values in the Inside and Outside boxes.
Add a gutter margin for bound documents
A gutter margin adds extra space to the side margin, top margin, or inside margins of a document that you plan to bind. That helps ensure that text isn't obscured by the binding.
Click Page Layout > Margins > Custom Margins.
In the Gutter box, enter a width for the gutter margin.
In the Gutter position box, click Left or Top.
Note: The Gutter position box is not available when you use the Mirror margins, 2 pages per sheet, or Book fold option. For those options, the gutter position is determined automatically