You may have seen fine white lines appear when you print out a PDF proof of a page, and you may be afraid that they will appear in your job when your commercial printer prints it. There is an example below. Notice the fine white lines on the right side of the man on the purple background.

A white Lines  2

These are screen artifacts that are called stitching. Even though you can see them on-screen, they should not be a problem when printed at high resolution. They are caused because your artwork contains transparency. In the picture above you see that an outer glow has been applied to the image, which is a form of transparency. If you choose a method of creating a PDF file which requires transparency to be flattened these artifacts will appear because the flattening process breaks artwork into sections. This could happen if you created a PostScript file and then used Adobe Acrobat Distiller to create the PDF, or if you had chosen Acrobat 4 compatibility when you export to PDF. Both of these methods require transparency be flattened. You can avoid flattening transparency and artifacts if you export PDF directly from your application and if you choose Acrobat 5 compatibility or higher in your export settings. Check with your commercial printer about the proper PDF presets to use for their production process. But, in any case, even though you see the artifacts, they should not print.