An upload form that just says "invalid file" or silently refuses to accept a document is one of the more frustrating parts of dealing with any online application — job portals, government forms, visa applications, school registrations. The good news is the list of actual causes is short, and almost always one of the five below.
1. The file is over the size limit
The most common cause by far. Many forms state a limit right next to the upload button — "max 2MB," "max 100KB" — but it's easy to miss, especially if the limit is unusually strict. Photo ID uploads in particular are often capped surprisingly low (50-300KB), far below what a modern phone camera produces by default. Check the stated limit first, then compress to a target under it rather than guessing — a target-size compressor handles exactly this.
2. The file format isn't accepted
A form that asks for a JPG will often reject a PNG, HEIC (the default format on many iPhones), or PDF, even though all of them are technically images or documents. HEIC is a particularly common snag — it's the default photo format on recent iPhones, and a surprising number of web forms still don't accept it. Converting to plain JPG or PNG before uploading solves this instantly.
3. The dimensions or aspect ratio are wrong
Some forms — passport and visa photo uploads especially — require an exact pixel size or a square aspect ratio, and will reject a technically-valid, correctly-sized-in-KB image simply because the width and height don't match. This is a separate requirement from file size, and it's worth checking both explicitly — see the passport & visa photo size guide for how these two requirements interact.
4. The PDF is password-protected or has broken structure
A PDF that was exported oddly, edited in an unusual tool, or password-protected can sometimes fail an upload check even though it opens fine on your own device. If a PDF upload keeps failing for no obvious reason, try re-exporting or rebuilding it — converting it to images and back into a fresh PDF, for instance, produces a clean, standard file that sidesteps whatever structural quirk was causing the rejection.
5. The filename itself is the problem
Less common, but real: some older or poorly built upload systems choke on filenames with spaces, special characters, or unusual symbols. If nothing else on this list explains a stubborn rejection, try renaming the file to something simple — letters, numbers, and hyphens only — before uploading again.
A quick troubleshooting order
- Re-read the form's stated requirements carefully — size limit, format, and dimensions are often listed in small print near the upload button.
- Check the file's actual size and format against that requirement.
- If it's a size problem, compress to a specific target rather than a vague "make it smaller."
- If it's a format problem, convert to exactly what's requested, even if your current format seems close enough.
- If everything checks out and it's still failing, try rebuilding the file from scratch (screenshot instead of a saved image, or rebuild a PDF from images) to rule out a structural issue.