PNG sources: screenshots, diagrams and exported pages
PNG is the format of screenshots, chart exports, whiteboard app pages and anything else that is drawn rather than photographed. It is lossless and often has a transparent background. Turning a set of these into a PDF is typically about hand-in: a sequence of app screenshots for a bug report, exported slides for a reviewer, wireframes for a client who does not open image folders, or a chat transcript kept for the record.
What changes inside the PDF
The converter draws each PNG onto a canvas at full resolution and encodes the result as JPEG at quality 92 before placing it on its own page. Two consequences follow. First, the PDF is not lossless. JPEG at 92 is gentle, and on screenshots it leaves text readable and interface edges intact, but if you zoom to 400 percent you can find faint ringing around sharp black text on white. For a document meant to be read, not pixel-inspected, this is a fair trade for a much smaller file.
Second, and more important: transparency does not exist in JPEG, and the canvas fills transparent regions with black when it produces a JPEG. A logo or diagram with a transparent background will appear on a black page. If the PNG has any transparency, flatten it onto white first. The easiest route on this site is to convert it with PNG to JPG, check the result looks right, and then build the PDF from those JPGs. Screenshots from most operating systems are fully opaque and need no preparation.
Page size follows the pixels
Each page takes the exact pixel dimensions of its image and is landscape or portrait accordingly. A 2560 by 1440 screenshot becomes a wide page; a 1170 by 2532 phone capture becomes a tall one. Mixed orientations in one file are allowed and simply alternate. A PDF viewer scales pages to fit, so this reads fine on screen. For printing, the viewer will shrink each page to the paper; if the text becomes too small, print two pages per sheet or crop the screenshots tighter with the crop tool before converting.
A worked example with a set of screenshots
Eight desktop screenshots at 1920 by 1080, about 350 KB each as PNG, add up to 2.8 MB of images. After JPEG encoding at 92 each page is typically 200 to 400 KB, so the PDF lands around 2 to 3 MB. Screenshots with large flat areas compress much better than ones showing photos or gradients. Compressing the PNGs beforehand does not help much, because they are re-encoded anyway; reducing their pixel dimensions does. These are typical figures rather than guarantees.
Ordering, naming and limits
Pages appear in the order the files were added. The tool does not sort by filename, so if you select files in a picker that lists them alphabetically you get alphabetical order, and if you drag them in a different sequence you get that sequence. The download is always named images.pdf. Everything runs on your device with nothing uploaded, which also means the limiting factor is memory: dozens of 4K screenshots may be too much for a phone. There is no text layer in the output; a screenshot of text is still a picture. For searchable text, run the images through the OCR tool.