Designs that use graphics and text elements (basically any non-photographic content) are best supplied as vector PDFs. Portable Document Format (PDF) is a file system that contains all the information it needs to be viewable on any computer without additional software.
Images are dealt with in two different ways within a PDF, raster and vector. Raster images are basically dot matrix in structure and when you enlarge them there is a corresponding loss in image quality. Vector files are not resolution dependent, they can be scaled to any size without loss of quality, and this will ensure your design prints as sharp as possible. This is why we recommend vector over raster.
Vector graphics can be scaled to any size without loss of quality, whereas raster will become pixelated around the edges if enlarged.