Most printers are unable to print right up to the edge of the paper. You can choose how this unprintable area is shown by EscapeE 'eE' iconEscapeE: select Unprintable area from the 'View' menu, then choose an option from the sub-menu

Crop Does not show anything that falls outside the printable area of the page – any items outside this are not shown, so the unprintable area is left blank.
Outline the valid region Always shows the limits of the unprintable area, depicted by a dotted rectangle. If there are items in the unprintable area, these are also shown.
Outline if not blank Only shows the limits of the unprintable area when there are items in it (these are also shown).