A primary layout is the default layout that you set for the work environment. It lets you generate output without specifying additional options. The primary layout contains settings for the output type with which it is associated. It controls project windows, the table of contents properties, and other project entities.
1)In the Single Source Layouts pod, right-click a layout.
2)Select Set As Primary Layout.
The primary layout is labeled in the Single Source Layouts pod.
note: If you create new windows, the window type is based on the default layout. For more information, see this article.