Change InDesign CS5 Document Setup
After creating an InDesign Creative Suite 5 document, you can still make changes to its original document setup. To change the size of pages or the number of pages in an InDesign CS5 document that’s already open, use the Document Setup dialog box.
Choose File→Document Setup.
The Document Setup dialog box opens.
You can change the value in the Number of Pages text field if you need the number of pages in your document to be greater than or less than the current value.
The number of pages in your document updates after you close this dialog box. You can also change this number later by choosing Layout→Pages→Insert Pages or by using the Pages panel.
Select a new option from the Page Size drop-down list or manually enter values into the Width and Height text fields to change the page size.
You can also click the up and down arrows in the Width and Height text fields to choose a new value.
Click the Portrait or Landscape button to change the page orientation.
The page orientation updates in the workspace after you close this dialog box.
Click OK when you finish changing your document setup.
The modifications are applied to the open document.
If you make changes to the Document Setup dialog box when you have no documents open, the changes become the default settings for all new documents you create.