I think you are referrinng to the content area. This is the area where objects are placed. This content area is defined on the master page. By default there is a .5 in margin around the whole page. In the hierarchy view, expanf the MasterPages node, then the Page1 node. There will be an obejct called contentarea. Choose that object. You should see it highlighted in the drawinng area. Now you can resize the content area to fit your need....or you can go to the layout tab and set the width and height fo the contentarea if you prefer that way.
