Hi,
The default Realistic Visual Style can be tricky with creating PDF or hard-copy prints. I would suggest you try exploring your Visual Styles and their default settings. I ALWAYS suggest saving any changes to the default styles to newly named Visual Styles that suit your taste so that you can always use the defaults as a launching point for future issues.
I am almost certain that you will find your solution.
I am also attaching a helpful sheet on some issues I've worked through in Visual Styles to familiarize you with playing around with their settings.
There's plenty more content on this at Youtube and the Autodesk user help and tutorial resources.
Cheers,
Blaine
Blaine Young
Senior Engineering Technician, US Army