The file downloaded but will not open
Four quite different problems look identical from the desktop, and none of the fixes overlap. One size check rules out the most common cause in about ten seconds.
The download finished, the file is sitting there, and nothing will open it. Before assuming the sender made a mistake, it is worth working out which of four quite different problems you have — they look identical from the desktop and none of the fixes overlap.
1. The download was truncated
The most common cause. The connection closed early, the browser saved what it had, and you now own the first 60% of a file with the right name.
How to tell: compare the size on disk with what the sender says it should be. A transfer page usually states the size, and a mismatch settles it immediately. A file that is suspiciously round — exactly 2.00 GB — is also a clue, since that is a limit being hit rather than a file ending.
The fix: download it again, ideally on a wired connection, and do not put the laptop to sleep partway. If it fails at the same point every time, the stored file is the problem and the sender needs to send it again.
2. You do not have an application for it
Obvious once you see it, invisible while you are in it. A .psd, an .ai, a .sketch, a RAW file from a camera you do not own, a .dwg — these need specific software, and the operating system's error message rarely says so clearly.
The fix: ask for an export rather than the source. Nine times out of ten the sender assumed you had their toolchain, and a PDF or a JPEG is what you actually needed. This is the single most common miscommunication in file delivery — see sharing files with clients.
3. The extension is wrong or missing
Some paths strip or mangle extensions, particularly when a file has travelled through several systems. A file called report with no suffix will not open on Windows, which decides what to do from the extension alone.
The fix: ask the sender what it should be and rename it. This is safe — renaming does not change the contents — and it costs nothing to try.
Related trap: double extensions. A file arriving as invoice.pdf.zip is a zip, and a file arriving as invoice.pdf.exe is not something you should open at all.
4. It is encrypted and you have the wrong key
On an encrypted transfer, decryption happens in your browser before the file is saved. If the key is wrong, you should be told so on the page rather than handed a broken file — a correct implementation checks the key before it starts.
If you somehow end up with a saved file that is unreadable noise, the download went wrong rather than the key. Sealed chunks are authenticated, so a truncated or altered chunk fails to open rather than decrypting into garbage. That is why an error here is a good sign: it means the tampering or truncation was caught rather than passed on to you.
Zip files specifically
Archives generate their own category of trouble.
- "The archive is corrupt" nearly always means an incomplete download. Go back to point one.
- A multi-part archive —
.z01,.part1.rar— needs every part present in the same folder before any of them will open. Missing one is fatal. - RAR and 7z do not open natively on a stock Mac or Windows machine. You need software, or you need the sender to use zip.
- Files inside look odd on Windows — a
__MACOSXfolder, files starting with a dot — is harmless clutter from zipping on a Mac. Ignore them.
Media files that will not play
A video that opens to a black screen or refuses to play is usually a codec problem rather than a broken file: the container (.mov, .mkv) is fine but your player cannot decode what is inside. ProRes and other edit-grade codecs will not play in a standard player at all.
Try VLC, which handles nearly everything. If it plays there, the file is fine and the original player was the problem. If it does not, ask for an H.264 MP4 — see sending large video files.
A quick order of operations
- Check the file size against what the sender says. This one test rules out the most common cause.
- Download it again on a stable connection.
- Check the extension and what opens it.
- Try VLC for anything audio or video.
- Ask for a different format — usually the real answer, and never the embarrassing question people think it is.
Related: when a download link is not working covers the errors that happen before the file arrives, and why large uploads fail covers the sending end.
