The following is a useful guide to creating a successful PDF.
Always ensure that all images used within your document are in CMYK. If photographs have been taken using a digital camera they will natively be in RGB, which, while visually will look okay, when converted for printing may appear slightly 'flat'. It is recommended that all images are converted in Photoshop or similar application.
Always ensure that you have used true fonts and you have not italicised, outlined or made bold within the application as this may cause problems (even if all appears okay on your screen).
It is recommended that white out type should be a minimum of 6pt in size, and medium or heavier in weight.
Should you require large areas of solid black, it is adviseable to add a shiner. Do this by making a new colour made from 40% cyan and 100% black. This will ensure that the black prints solid.
If you have used spot colours, they will be retained when creating the PDF. If you have used spot colours but are not printing the job in spot colours it is recommended that they are changed to process colours prior to producing the PDF to prevent confusion.