Lossless conversion of PNG to PDF

Lossless convert single PNG to PDF

convert in.png out.pdf

For single images I avoid -page letter as the image in general doesn’t fit to the page, leaving big margins.

Lossless convert many sequentially named/numbered PNGs to single PDF

This puts one image per page

convert -page letter -adjoin *.png joined.pdf

The -page letter does not upsize images, so tiny images will be tiny on the page, one image per page.