To export your Photo Book PDF, follow these steps:
1. Open your "Photos" or "iPhoto" application on your computer.
2. Select the Projects tab at the top and double-click the project you want to preview. Or select the project from the sidebar if it's visible.
3. Control-click or right-click inside the area surrounding your project (not on the pages themselves)
4. Choose "Save Book as PDF" from the dropdown menu that appears.
5. In the "Save As" dialog, give the file a name and choose a location to save it in. Then click "Save"