A font file overrides Font and Bold, and unlocks box-drawing and Unicode glyphs the built-in fonts cannot represent.

Invoice form lays two invoices onto a pre-printed form, every field landing inside a box somebody else drew. That is the hard case, and the geometry was fitted to the form's own rules.
Statement run goes over a two-page letterhead, so page one gets headed paper and the rest continuation stationery.
Box-drawing report is 132 column output framed in characters no built-in font contains, so it loads a font too. Clear the font and render again to see exactly what the option is for.

All three are cp850 with an eject at each end, like a real print stream. Take the files and experiment: invoice.txt · invoice-form.pdf · statement.txt · letterhead.pdf · report.txt · dejavu-sans-mono.ttf (licence)