Download Ghostscript from a link such as:
www.ghostscript.com/download/gsdnld.html

Depending on your system select either Windows 32 bit or Windows 64 bit GNU Public License (GPL) as shown by the red boxes below. (To determine if you have a 32 bit or 64 bit system: click Start -> Control Panel -> System and Maintenance -> System, and then you can view the system type.)

Run the Ghostscript executable file. After installation, the Ghostscript website may open (and you may not receive any messages that the software was successfully installed), but you can then install Insert PDF.