I am trying to help with an .ai document I did not create. It has multiple layers and when they save as PDF, a faint black outline appears behind one of the images but an inch below it--just the outline of that image shape, not the shape itself.
Their concern is whether that outline, which is not intentional, will appear when printing. Obviously the best thing would be to figure how to remove/prevent it, before sending to printer.
I am a novice as you can tell, just cracking into Illustrator, and the complexities are many...
How can I try to fix this issue?
Do I need to fix it, will it show when printing?
Since the file contains lots of linked images, do I need to update every single link for viewing on my own computer before I can even try to recreate the ghost outline effect bug?
Depending on the PDF export settings you're using, it may be due to transparency flattening. This is often apparent when using X-1a, specified by many print providers. If you zoom in to examine, those lines generally disappear (and PROBABLY won't affect press output), but can still be annoying.
One way around this is to create a solid color-filled object (say process white or black), and place it at the very back. In most situations, it should resolve things. You may have to experiment a bit, to get the desired result.
This same process can be applied to InDesign, as well.