Work from the cheapest test upward: try a second reader, then check the file size. A file that is 0 KB or far smaller than expected never finished downloading, which is the most common cause by a distance. If a password box appears, the file is fine and you need the password.
Runs in this tab, on pdf-lib, qpdf (WebAssembly) and pdf.js, so your file is read from your own device and never sent anywhere. Check it yourself
How do I fix it?
1Try a different reader firstDrag the file onto a browser tab. Chrome, Edge, Safari and Firefox all have their own PDF engines and are more tolerant than Acrobat of a slightly malformed file. If it opens there, the file is fine and the reader was the problem.
2Check the file sizeRight-click and look at the properties. 0 KB, or a few kilobytes where you expected megabytes, means the download failed. Download it again — that fixes this case outright.
3Look at the first bytesOpen it in a text editor. A real PDF begins with %PDF-. If you see HTML, or the word "PK", it is a web page or a ZIP with the wrong extension, and renaming it correctly may be all it needs.
4If you get a password box, find the passwordEncrypted statements usually say the format in the covering email: date of birth, a postcode, the last digits of an account number. The file is not broken.
5Ask for it again before trying to repair itA fresh copy from the sender solves a truncated or damaged file in seconds and costs nothing. When the original is gone, Repair PDF rebuilds what can be rebuilt.
Why does this happen?
The download was cut short. An interrupted download leaves a file that looks right in the folder but is missing its end. A PDF stores its index at the end, so a truncated file has nothing to read from.
It is encrypted, not broken. A password prompt means the file is intact and the content is encrypted. That is the file working as intended, not a fault.
It is not actually a PDF. Files saved from a web page or a mail client are sometimes an HTML error page or a ZIP with a .pdf name. The reader opens it, finds no PDF header, and refuses.
The reader is blocking it. Acrobat’s Protected View and enterprise policies block files from the internet or from network drives, often with a message that sounds like corruption.
The file is genuinely damaged. A bad transfer, a failing drive or a crash during save can leave a structurally broken document that no reader can parse.
Questions
My PDF opens in Chrome but not in Acrobat. Why?
Chrome’s engine tolerates errors that Acrobat rejects, and Acrobat also applies Protected View to files from the internet. Try printing to a new PDF from Chrome, or clear the file’s "downloaded from the internet" mark in its properties.
What does "the file is damaged and could not be repaired" mean?
The reader could not find or follow the cross-reference table that says where each object lives. That is usually a truncated download rather than deep corruption — re-downloading fixes it far more often than repair software does.
Is a 0 KB PDF recoverable?
No. There is nothing in the file at all — only a name. The only route is another copy.
Can I fix a broken PDF here?
Yes. Repair PDF checks the file first — whether it is really a PDF, whether it was cut off, whether it is only encrypted — then rebuilds it and tells you how many pages open afterwards. It runs in your browser, so nothing is uploaded.
Why won’t my PDF open in Chrome?
Usually a setting that downloads PDFs instead of showing them, an extension, or a form built in an older Adobe format. PDF won’t open in Chrome goes through each.
Why won’t a PDF open in Preview on my Mac?
Preview shows a blank window or quits on PDFs it can’t parse — usually a damaged file, or a dynamic XFA form only Adobe Reader can show. Try the file in Chrome; if it opens there, Preview is the problem. If it fails everywhere, repair it.
Why won’t a PDF attachment open in Outlook?
Outlook opens attachments in a protected preview, and some mail systems block or alter PDFs on the way. Save the attachment to your computer first and open it from there; if it is 0 KB or tiny, ask for it to be sent again.
What does “not a supported file type or has been damaged” mean?
Adobe can’t read the file as a PDF: either it isn’t one (a web page or Word file with a .pdf name), or it was damaged — often by an email attachment that wasn’t decoded correctly. Repair PDF tells you which it is.