When you choose in Adobe Acrobat - Edit - Preferences - Page Display - and untick "smooth line art" the thin lines on the area fill disappear. If I leave it on, it appears. But me personally, use the PDF straight from Chief Architect and open in Photoshop for some design work, and the lines are there, unless I untick the anti-aliasing option which makes the text look rough and not smooth... also tried it in Chrome browser, and same lines appear, so I think the problem is still on the Chief side, the way it writes the PDF somehow....