When you create pages that contain transparent objects (drop shadows, glows, feathers, bevels, blend modes, etc.) in InDesign, you may get unexpected results when you make a PDF file and view it in Adobe Acrobat or Adobe Reader.
One thing that can go wrong is that you might see very thin vertical or horizontal white lines in your images. These lines are no cause for panic. They are just an on-screen anomaly in Acrobat. The lines will not print, and they will only be visible on the screen if you:
a) print to PostScript or the Adobe PDF driver to create the PDF file
b) choose File > Export in InDesign to create the PDF file, and choose Acrobat 4 (PDF 1.3) for the Compatibility.
If the lines bother you on the screen, you can make them disappear in Acrobat by choosing Edit > Preferences (Windows) or Acrobat > Preferences (Macintosh). Select the Page Display category, and deselect the Smooth Line Art option.