The Settings->Paper submenu allows you to change the paper size and orientation. In addition, Settings->Paper->Show Margins toggles between showing and hiding the printer margins, but note that this facility is not available if you use the -disable_print command line argument.
The predefined paper sizes A0 to A5, letter, legal and executive can be selected from the Settings->Paper menu. Other paper sizes can be selected from the dialog box displayed using Settings->Paper->Other. Select the radio button labelled Predefined to enable a list of additional known paper sizes or select the radio button labelled User to enter a custom size.