Some things to take a look at:
Object Styles (Here you can make lines bolder or thinner both in projection and in cut views)
View Scale (The bigger your drawing, the "thinner" it will appear. It's a proportion thing, since the same weight is being used in bigger sheets)
and if you use Revit 23:
PDF Export (Check if you're using vector processing instead of raster)
Cheers.
Architecture Modelling, BIM Workflows and Information Exchange.
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