Jim Thompson said:
The PDF looks significantly sharper.
And herein lies the key.
A PDF, properly generated from schematics, is a LINE DRAWING. Well,
and other shapes too, including text. The contents of the file are
the endpoint coordinates and the line style (or other *description* of
the elements, not a *photo* of the elements), so the line looks like a
nice clean line no matter the resolution of the device you're viewing
it with, or any magnification. Text has smooth anti-aliased edges
regardless of how you view it. Etc.
A PNG is a raster. You can make a PNG smaller than the PDF by simply
choosing a lower resolution, but then your line turns into a row of
squares at higher resolution or magnification, and printouts may have
that "stairstep" look.
So, *if* your software generates a PDF that truly is a line drawing,
and not a pdf-wrapped raster, you're better off keeping it that way so
it doesn't get pixelated. If, however, your software just wraps a
raster in a pdf (you can tell by zooming way in and seeing if the
lines remain lines, or become blocky), then you may be better off with
a PNG.
Now, considering that most schematics have primarily vertical and
horizontal lines, which PNG handles well, the benefits of PDF may not
be apparent. If you want to see what/if the differences are, choose a
test schematic that has many diagonal lines, curves, and text.
