PDF to PNG

A PDF page containing body text, tables, forms or line diagrams is exactly the content JPEG compression handles worst, because its algorithm identifies and discards the kind of high-frequency detail that sharp character edges are made of — the result is a faint but real halo or softness around lettering, most visible on small text and on anything zoomed in past its original size. PNG carries no such penalty at all, because it stores every pixel exactly rather than discarding any of them, which is precisely what a page whose value is its crisp readable text or clean vector lines actually needs.

The trade for that fidelity is size: a PNG rendering of a text-heavy page is routinely several times larger than the equivalent JPG, because text and line art produce exactly the kind of sharp, high-contrast edges that resist the redundancy PNG's compression relies on. That is a reasonable cost for a page whose whole purpose is to stay legible, and an unnecessary one for a page that is mostly a photograph, where JPG will look just as good at a fraction of the size.

This preset stays at 150 DPI rather than jumping to 300, because the case it targets — needing crisp lossless output for text or diagrams — is generally about screen legibility rather than print reproduction. If the images are also headed to print, raising the DPI alongside choosing PNG combines both concerns, at the cost of a larger file than either choice would produce alone.