Quality

Why the result can look soft

A PDF page is drawn at whatever size you ask for; an image has a fixed number of pixels. The export has to pick a number.

Pick too few and small type turns to mush. Pick too many and a single page becomes a file nobody wants to receive. Most exports aim at the middle, which is right for a page being viewed and wrong for a page being enlarged.

What you can influence

The content of the original. A page built from text exports cleanly at almost any size, because the letters are drawn fresh each time. A page that is itself a photograph of a document exports exactly as badly as the photograph was — the conversion cannot invent detail that was never captured.

The thing to check

Look at the smallest type on the result at full size. If a footnote is readable, everything above it is.