Gutter margins are extra space on the inside edges of book pages. This extra space prevents content from disappearing into the binding / spine of the book.
Many document programs allow you to set a gutter or inside margin while setting up your document size, but you can also add it after the fact using Adobe Acrobat. This is especially useful when merging documents, duplicating pages, and changing the order of pages, when what was an odd page may now be an even page (gutter is on different side).
How to add margins to a PDF in Adobe Acrobat
- Open final PDF in Adobe Acrobat
- Click Organize Pages on the sidebar
- Click More > Set Page Boxes on the toolbar
- In the Change Page Size section…
- Click Custom
- Enter the page width and height
- In the XOffset box, enter the amount of gutter margin, e.g. .125
- In the Page Range section…
- Click All
- Set Apply to: as Even Pages
- Click Ok
- Repeat steps 3-6, except make the margin negative (e.g. enter -.125) and apply to the odd pages.