Apply page scaling factor removes the page scaling factor and scales the page to compensate.
A page of 10 by 10 inches and a page scaling factor 2 will be displayed and printed as a page of 20 by 20 inches. By applying the page scaling factor, the actual page size will become 20 by 20 inches.
Page scaling has been introduced in PDF 1.6. If the page scaling factor is not removed or applied, the page size can only be displayed correctly in Acrobat 7 or higher.