There seems to be something missing from your printing interface. This is how mine looks:
Yours does not give a choice between “Viewport”, “Extents” and “Window”, and as you can see the latter gives a similar result to your version, i.e. the scale is set as “Scaled to Fit”, yet the picture does not extent to the full page size.
It appears that the “Window” choice asks for a window to be set around your objects, meaning that the printing resolution will be applied to the entire window setting. This could explain the bad resolution of your pdf, when for some reason a large window has been set around your objects.
Edit: I see that your 1:1 scale picture shows the objects filling the entire sheet, which sort of dispels my theory. But the missing input fields still remain mysterious…