after converting pdf to autocad , the circle and curves were seen as set of tangent lines ,sharp corners were seen
It may just be your display settings in AutoCAD. I have to adjust those every time I open the software. Do the following and it should fix the problem.
In the command bar, type options.
Then go to the display tab that in the screen that opens at the top.
In the top right of the display tab, you'll see a display resolution area with four options to change. I always set them to the following.
10000: Arc and Circle Smoothness
100: Segments in polyline curve
2: Rendered Object Smoothness
100: Contour lines per surface
That should make it appear much better. If it doesn't let me know.