When you are working with PDF documents, it is often required to merge them together, rotate some pages or select some of them, etc. This functionality is helpful when you care about the nature and want to avoid printing some pages. It is quite often when some authorities ask you to print a PDF document, sign just one page and send them back a scanned copy. In this situation, the PDFtk utility can be very useful. In this article, I describe some commands I use from time to time.