PDF (portable document format) the definition of a pdf is basically a secure file format that can be saved from almost any application. The file has a number of forms of compression, which allows the file to be considerably less in size to that of the source files. When you distill or print to pdf the distiller takes all the information it requires to print the file independently of the orginal files. The finished size of the file can be minimised depending on the destination of the pdf. These files can be smaller for e-mailing to clients for ‘passes on text‘ (which is known as soft proofing) because the file is only going to be viewable for screen, the images only need to be low resolution making the file alot smaller than is required for final output. Another major advantage the pdf has over other file formats, is that it is platform independant which means as long as the viewer has Acrobat Reader installed on their machine they will be able to view your file regardless of what platform you distilled it on, be it a Mac, PC or Unix based machine.