Are you using vector-based software such CorelDraw, Adobe Illustrator, Adobe InDesign, or Adobe Freehand? For vector files such as these all text must be converted to outlines before creating the file (preferably PDF) you send us.
Are you using a bitmap-based (a.k.a. raster) software application such as Adobe Photoshop? For bitmap files such as these, simply flatten the image. Avoid font sizes smaller than 8 pts or fonts that are very narrow as these may not print, or will lack crispness, or may not display well against dark.
