When reviewing eproofs and PDFs, you will often see hairlines. These thin, light-colored lines are a result of a transparency flattener used by PDF creators and will sometimes appear around text boxes and masked images. Fortunately, these hairlines are only visible in your PDF and will not print when the book is produced. These lines may appear on both cover and interior files.
Hairlines may also present themselves in additional ways. If you have any concerns, it’s advisable to review your native working files to ensure the lines aren’t present. You may also order a printed copy of your book for review.