It is oboviously desirable that documents on the Internet are printable on all continents. This paper gives advice on how to achieve this. The reason why you have to add 18 respectively 6 mm to both the top and the bottom margin is that you do not know what kind of printer the recipient uses, and different printers feed paper in different ways, requiring the margin to be added either at the top or the bottom of the paper. Left and right margins on any paper format should be at least 20 mm wide to accomodate filing with ISO 838 hole punches. Ensure that also headers, footers, and page numbers are within the suggested minimal margins.
Many word processors put headers, footers and page numbers outside the specified text margins.
Many programs for printing Postscript files do not allow this. In that case, the recipient can convert a Postscript document to PDF format and then print it with the PDF printing program. This requires, however, that the recipient has the Adobe Acrobat Distiller program, which is not freeware. Recent versions of the freeware ghostscript can also convert to PDF format. The user may also have to specify the paper size as the actual paper size loaded in the printer, not the paper size specified when the document was converted to PDF or Postscript format.