Line Thickness

Hi I am new to DraftSight and after playing around with the software my initial impressions are good.

I do have one query though:

Can anyone explain why the lines I have drawn end up looking thick when converting into pdf format?

I have made sure basic things like line thickness and lightweight aren't the problem so don't understand why this is happening.

In model and paper space lines look fine (thin) but when I go to print to pdf the lines appear very thick in print preview and also in converted pdf file.

Thanks for any assistance!!