Unwanted dots appear in pdf when converted from Microstation v8i ss4 dgn

I am using microstation v8i ss4 I get these unwanted dots in pdf when converting the dgn to pdf. These contents were converted from suppliers pdf drawing to dxf and then taken into dgn. When I print the pdf the unwanted dots appear. How can I hide or remove these dots.

In dgn the dots are not visible.

Can anybody suggest me an idea to clean these dots.