What HEIC actually is
iPhones have saved photos as HEIC by default since iOS 11 came out back in 2017. HEIC stands for High Efficiency Image Container, and under the hood it's using HEVC — the same compression that powers most 4K video streaming — just applied to a single frame instead of a whole video. That's the entire reason it exists: a HEIC photo looks about the same as a JPEG while taking up roughly half the space. It's a genuine technical upgrade, not some Apple trick to save server costs.
Problem is, "more efficient" and "everyone can open it" are two completely different things. JPEG has been around since 1992, and pretty much anything with a screen can display one. HEIC is newer, it's wrapped up in patent licensing, and support for it landed on different platforms years apart from each other.
Why it keeps causing problems
Macs and recent Windows versions open HEIC fine these days (Windows usually makes you grab a free codec pack from the Microsoft Store the first time you try). Most newer Android phones and Google Photos handle it too. But a surprising amount of ordinary software still trips over it — web forms that only take "jpg or png," older editing tools, printers with a direct-upload feature, plenty of business systems nobody's gotten around to updating.
So when someone can't open a photo sent from an iPhone, nothing's actually broken. The file is fine. It's just written in a language the app on the other end never learned to read.
How to actually fix it
Easiest fix, and it needs zero extra apps: on the iPhone, go to Settings → Camera → Formats and choose "Most Compatible." Every photo from that point on saves as a normal JPEG instead. For pictures you've already taken, sending them through AirDrop, iMessage, or email to a non-Apple device usually converts them to JPEG automatically during the send — you don't have to do anything else.
If you need to convert files already sitting on your device, the Photos app can export as JPEG (File → Export, on a Mac). iOS itself, annoyingly, doesn't give you a one-tap "convert to JPEG" button outside of sharing or exporting — so the share-sheet trick above is usually the faster route.
Getting these into Image → PDF
Our Image → PDF tool takes JPG, PNG, and WEBP right now — not HEIC, since decoding it isn't supported consistently enough across browsers to rely on yet. Switch your camera format or export/share the photo first, either trick takes a few seconds, and then it drops into the converter just like anything else.