problem in font view when export from indesign to PDF

Hey,

When I export from indesign cc 2015  to PDF (acrobat DC) windows 7, I get this underlines /shadows under the text.

never ever had this problem before. Even when i enlarge the view to 1200% i still see it - it's ODD!

both in white and black as you can see. it's all process colors, no transparency.
when i print it - it's fine (in a laser printer).

Any idea of why does this happen and how can it be solved?

will appreciate any tip on that.

thanks in advance!

Hagit.