The zoom applies to the active worksheet.

New worksheets open using the default magnification set in the Tools>Options>Interface tab Default zoom drop-down list. If a worksheet was saved with a zoom factor of other than 100%, then that worksheet opens with the saved factor and not the default value.

If you apply the zoom factor to an active help page in the Help Navigator, the magnification applies to all help pages viewed in the Help Navigator.

If you set your Maple session to use multiple help navigators (Tools>Options>Interface tab>Multiple Help Navigators check box) then the zoom factor applies only to the help pages in the specified navigator.