Changing preview images By default, the PDF Preview Bar displays the PDF at 15% of actual size. You can also view the preview in greater detail. To enlarge preview images Click the plus sign button at the top of the PDF Preview Bar. The preview will increase from 15% to 30% of actual size. Click the plus sign button again to increase the preview size from 30% to 45% of actual size. Click the minus sign button to reduce the image from 45% to 30%, then 30% to 15% of actual size.