The message is Adobe’s catch-all, and the words after it say why: the file is damaged, access was denied, or it isn’t a real PDF. Open it in Chrome or Edge first. If it opens there, the problem is Reader; if it fails everywhere, the file is damaged and Repair PDF can usually rebuild it.
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?
1Open it in a browserDrag the file into Chrome, Edge or Safari. If it opens there, the file is fine and Reader is the problem: update it, or keep using the browser to view it.
2Check the size and download it againA file that is far smaller than expected, or 0 KB, didn’t arrive whole. Download it again or ask the sender to resend it, ideally as a link rather than an attachment.
3Move it somewhere simpleFor “Access denied”, close any app that has the file open, copy it to your Desktop or Documents folder, and give it a short name without symbols. Then open the copy.
4Repair the fileDrop it on Repair PDF and press Repair PDF. It checks whether the file is really a PDF, rebuilds a broken index, and recovers every page that can still be read — in your browser, without uploading it.
5If it isn’t a PDF at allRepair PDF says what the file really is — a web page, a ZIP, a Word document — so you know to ask for the right file instead of trying to fix the wrong one.
Why does this happen?
“The file is damaged and could not be repaired”. The PDF is incomplete or corrupted: a download that stopped early, an attachment that was decoded wrongly, a file copied from a failing USB stick. The end of a PDF holds the index Reader uses to find every page, so a file cut short often loses exactly that part.
“Access denied”. Reader can see the file but isn’t allowed to read it. Common reasons: it is still open in another program, it sits in a synced or network folder that hasn’t finished downloading, or Reader’s sandbox (Protected Mode) is blocked from that location.
“Not a supported file type or has been damaged”. The file has a .pdf name but isn’t a PDF. A web page saved under a .pdf name, a Word file renamed by hand, or a portal’s error page downloaded instead of the document all trigger it.
The file is 0 KB. Check the size in File Explorer or Finder. A zero-byte file is empty: the save or the download never wrote anything, and no tool can recover pages that were never there.
An outdated Reader. Very old versions of Reader can fail on files made with newer features, such as some kinds of compression and encryption. Updating fixes these; nothing is wrong with the file.
Questions
Why does the PDF open in Chrome but not in Adobe Reader?
Browsers’ PDF viewers are more forgiving of small errors, and they don’t use Reader’s Protected Mode. If Chrome shows it, the content is intact; update Reader, or repair the file so every viewer accepts it.
Can a PDF damaged by a failed download be fixed?
Often, yes. Repair PDF reads the file from start to finish instead of trusting its index and writes a fresh one. Pages the download never delivered can’t be recovered, though.
Is it a virus if a PDF won’t open?
Rarely. Damaged downloads and renamed files are far more common. If the file came from someone you don’t know, don’t try to repair it — delete it.
Do I need Adobe Acrobat Pro to repair a PDF?
No. Acrobat Pro has no dedicated repair button anyway; it tries to fix files as it opens them. Repair PDF is free and runs in your browser.