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.
Solution 1: Export as PDF 1.4 or later
In the Export Adobe PDF General settings, select Acrobat 5 (PDF 1.4) or higher from the Compatibility options.
Solution 2: Convert spot color to process color
1- Choose Window > Swatches to open the Swatches palette.
2- Double-click the spot color to open the Swatch Options dialog box.
3- Choose Process from the Color Type pop-up menu.
Solution 3: Move the spot color to the top of the layer
Change the stacking order of the objects, so that the object with the spot color is at the top, before flattening the image.
1- Select the object.
2- Choose Object > Arrange > Bring to Front.
Solution 4: Use layers to arrange the colors
Place the spot colored object on a different layer, then arrange that layer above the layer that contains the transparent objects.
Solution 5: Set the opacity for the spot color to less than 100% and export to PDF again
If your print shows dark lines on the printout of a created PDF file, then lower the opacity and create the PDF file again.
1- Select the object that contains the spot color.
2- Choose Window > Transparency to open the Transparency palette.
3- In the Opacity field, enter a value like 99.9%.
4- Export or print to PDF again.
Additional Information
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.
