There are DLL’s that are used to create the PDF file. And in those DLL’s is “hardwired” code that sets the various parameters of the PDF.
I only know this because during one version update, those DLL’s changed the scaling used to render the PDF. Something along the lines of old version rendered the PDF to default to printing at 100% scale, while the new version caused printing to be “Shrink to fit” This caused problems on pre-printed forms like checks. That thread may have insight into what other PDF settings are controlled by the DLL.
edit
Here’s the thread. Not as much internal info about the DLL’s as I thought.