Rasterized PNG, JPG or TIFF files are necessary. If you file is a PDF or vector file (such as Corel Draw or Adobe Illustrator), please convert it. You will need to make these changes before submitting these files for accurate color when printed due to different CMYK and RGB outputs. For instance, many programs like Adobe Illustrator will default to a CMYK color space. Its relatively easy to change it to RGB so make sure you do so before saving a jpg or tif version of your file.