When you export to Adobe PDF from InDesign, white or dark lines are visible in the PDF file. One or more of the following is true:
- White or dark lines appear in areas where process colors and spot colors interact during flattening.
- You have an image file behind objects or text that have transparency applied, including drop shadows.
- You exported with Acrobat 4 (PDF 1.3) compatibility.
In the Export Adobe PDF General settings, select Acrobat 5 (PDF 1.4) or higher from the Compatibility options.
Change the stacking order of the objects, so that the object with the spot color is at the top, before flattening the image.
Place the spot colored object on a different layer, then arrange that layer above the layer that contains the transparent objects.
If your print shows dark lines on the printout of a created PDF file, then lower the opacity and create the PDF file again.
White or dark lines can be caused by anti-aliasing of an application where the two regions intersect. Turning off the anti-aliasing in Acrobat's display preferences (Smooth Line Art/Smooth Images) eliminates these lines.
Acrobat 4 PDF compatibility (PDF 1.3) does not support transparency. Therefore, InDesign flattens the file during the conversion process. Consider changing the settings in the Transparency Flattener presets.
Converting the spot color to a process color allows InDesign to flatten the image without stitching. By moving the spot colored object to the top of the stacking order or moving it to a different layer, you can also prevent stitching.
White lines are likely to be only a display issue in Acrobat. They do not appear when you print a file.
Dark lines are likely only to occur when you print a file. Setting the opacity can create white lines when you view a file in Acrobat, but these white lines don't print.