PNG is what screenshots, diagrams, charts and exported designs come out as, and PDF is what people are asked to submit. This turns a folder of the former into one of the latter, with the image data embedded exactly as it is.
Genuinely lossless
PDF can carry PNG image data natively, so the compressed bytes go straight into the document. Nothing is decoded, re-drawn or re-compressed on the way in. A screenshot with crisp text arrives in the PDF with exactly the same crisp text — which matters, because the most common thing to convert this way is a screenshot of something someone needs to read.
Watch out for tools that convert PNG to JPEG internally to save space. It is a reasonable-sounding optimisation that ruins screenshots, since JPEG blurs the sharp edges that make small text legible.
What happens to transparency
PDF supports transparency, and it is preserved in the file. But a PDF page has no background of its own — readers draw white behind it — so a transparent PNG looks as though it is on white when you open the document, and prints on whatever colour the paper is.
The thing to know is that transparent areas will not stay transparent if the page is later printed onto coloured stock or placed into another document with a dark background. If the image needs a definite background, set one before converting rather than assuming the PDF will supply it.
Page size, and when to set one
- Leave it unset and each page is made exactly the size of its image. Nothing is scaled or cropped, and a screenshot appears at its true pixel dimensions.
- Choose A4 or Letter when the document will be printed or submitted somewhere expecting standard paper.
- With a page size set, each image is centred with a margin and scaled to fit, keeping its proportions.
- Mixed sizes are fine either way — a wide chart and a tall screenshot each get sensible treatment.
File size expectations
PNG is not an efficient format for photographs, and a PDF made from photographic PNGs will be large. If your images started life as photographs, converting them to JPG first and then to PDF produces a dramatically smaller document at a quality nobody will notice. For screenshots and diagrams, stay with PNG — the file is usually small already and the sharpness is the point.
The order of the list is the page order, and the arrows change it. Everything runs in this tab, so nothing is uploaded regardless of how many images you add.