When you create a booklet, it's best to start with a new, blank document so that you have better control over the placement of text, graphics, and other elements. You can add a book fold to an existing document, but you may have to reposition some elements once the book fold is in place.
If your document is not set to landscape orientation, Microsoft Word sets it to landscape.
If you need even more space along the fold to accommodate binding, type or select the amount of space you want in the Gutter box.
If the number of pages in the document exceeds the number of pages you select for a booklet, Word prints the document as multiple booklets.