Multipage pdf to series of pngs with transparency

pdftocairo is part of the poppler-utils package.

pdftocairo -png -transp -scale-to 2048 in.pdf out

Larger of width or height will be scaled to 2048px.
Output will be series of png’s, like:

out-01.png
out-02.png
out-03.png
...

Man page.