In general, digital printing does not need extreme resolutions. For photographs, make sure the resolution of your file is over 150 DPI at the maximum print size. For other images, especially with text or line art, use a resolution that is higher: say, about 220 DPI at least.
In PDF documents, the same rules apply. Take note, that the dimensions of the document define the maximum print size, so the DPI of any embedded images must be calculated with respect to the height and width of the source PDF. Please use text for text (so do not convert your text to images - that has nearly always a bad result).