Displays the XML source code that describes the structure of the form design and its objects. It is recommended that you do not edit the XML source code directly.
Livecycle win layouteditor Layout Editor 
By default, not all the tabs are displayed. The Design View tab is displayed; however, the Master Pages tab and the XML Source tab are not displayed. The Preview PDF tab is displayed only when Acrobat or Adobe Reader is installed.
The pages in Design View contain a form design’s content. The first time you start LiveCycle Designer ES or create a new form design, the Design View tab displays a page ready for objects to be added.
Master pages specify the layout and the background for the form design. You add objects that will occur in the same position throughout the form design on a master page. The Master Pages tab is hidden by default.
As you work, if you have Acrobat or Adobe Reader installed, you can preview the form in the Preview PDF tab. Use the Preview PDF tab to view and test the operation of a form or template as if it were a PDF file. You can set options for previewing interactive forms or printable forms in PDF by using the Form Properties dialog box (Preview tab).
See also 

Layout Editor