Final Draft 9 has two paper sizes, US Letter and A4. To switch from one to another, go to Document > Page Layout > Margins tab and choose the size from the dropdown menu.
Note that in Final Draft 8 and older, the paper size for all scripts is determined by the paper size set by the computer's default printer settings. In Final Draft 9, the chosen paper size is embedded in each script and will open with that paper size no matter what the computer's default printer settings are.
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