Forms, visa and insurance portals, schools and employers routinely ask for a PDF rather than a picture, and they almost never accept HEIC. Putting the photo of a receipt, ID or signed page into a PDF solves both problems at once: the PDF opens on every device and prints at a predictable size.
Add several files and you can also combine them into a single PDF. The defaults suit most files. Under Options you can choose the page size and set the quality.
Most browsers other than Safari cannot read HEIC themselves, so a HEIC decoder of under 1 MB is downloaded the first time and kept in the browser cache. Each picture becomes one page. The page can match the picture's own size or be A4 or US Letter; on paper the sheet turns to suit the picture, which is shrunk to fit inside the margins and never enlarged.