PNG to PDF writes each PNG into its own PDF page, in the order you add the files. Screenshots, diagrams, and exports from a drawing app are usually PNG. Photographs from a camera are usually JPG. This page accepts both, because the underlying tool is the JPG to PDF converter and the only difference is the heading. Image to PDF is the third heading on the same converter, for people who have a mix and do not care which extension came first.
The browser reads the file locally. A PNG that is actually a renamed spreadsheet will fail, and the note will say which position in the list failed. Transparency is part of a PNG. The image is embedded as PNG rather than being flattened to JPEG on this page, so a logo with a clear background can stay clear in viewers that support it. If you later run the file through compress PDF, that step paints pages as JPEG and the clear background becomes white. Do that only if size matters more than the transparency.
Fit is the same rule as the main page. Pixels are taken at 96 per inch. Anything larger than A4 shrinks to fit, without stretching. Anything smaller stays smaller. One image is one page. Two logos side by side on a single sheet is not this tool. When the PDF is ready, the page count should match the number of files. Join that PDF to another document with merge PDF if a cover page has to come first. Shrink it only after reading the warning on compress PDF.
Nothing is stored. There is no sign-up and no expiring download link. Large screenshots of an entire desktop can be heavy. Convert them in batches if the tab slows down, then merge the batches. The image to PDF page is the same form if you arrived with both PNG and JPG in mind.