Very thin lines, called hairlines, are
problematic in offset printing. If left as is in PDFs, they might
not appear in the final printed piece. The Fix Hairlines tool can find
most hairlines and replace them with a heavier weight line.
Choose Advanced > Print Production > Fix
Hairlines, or select the Fix Hairlines tool on
the Print Production toolbar.
Enter a width for the hairline you want to find, and
enter a replacement width.
Adjust hairline widths using increment arrows. Shift-click
arrows to change widths by whole integers.
Select the unit of measurement from the Units menu.
(Optional) Select Include Type3 Fonts or Include Patterns
to replace hairlines in Type 3 characters or patterns with the same
replacement width as other hairlines.
Font characters and patterns can be used in a variety of
contexts in the same document (for example, different magnification
values), so changing the line width may produce unexpected results.
Check the results if you select these options, and adjust your selections
as necessary.