pdf: introduced a PreviewMargin property
pdf: introduced a PreviewMargin property

This is the margin of empty space around the preview page, so it stands away from
bounding widgets.

wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI