A PDF is usually "corrupted" for one of five reasons: the download was cut off, the file is not a PDF at all, it is password protected, its internal index is damaged, or some pages lost their data. The checker above identifies which, and its repair rebuilds the file while keeping every page that survived.
How to check a PDF
- Drop the PDF on the checker.
- Read the verdict and the list of checks: each one says what was found and what it means.
- If repair is offered, click it and download the repaired copy. Your original is never modified.
What the check looks at
- Is it really a PDF? The first bytes must carry the PDF signature. If not, we tell you what the file actually is: a web page, a Word document, an image.
- Is it complete? Every PDF ends with an end-of-file marker. Missing means the file was cut off in transfer.
- Is its index intact? PDFs keep a table of where each object lives. A damaged table is the most common "corruption" and the easiest to repair.
- Does a reader open it? We open it with pdf.js, the engine behind Firefox's reader, and report its version, page count, protection and forms.
- Does every page render? Each page is drawn from start to finish. Pages that fail are listed by number.
- Anything to be careful about? JavaScript, attached files, digital signatures and XFA forms are flagged, because each one changes what you should do next.
What repair can do, and what it cannot
Repair rebuilds the PDF from the objects that survived: a correct index, a correct ending, stray bytes removed. Text stays text, links stay links. That fixes most files that "will not open" or that a printer or signing service rejects.
When the structure is beyond rebuilding, a rescue saves every page that can still be drawn as an image, so you at least get something that opens everywhere. What it cannot do is invent data that is gone: if a download stopped at page 12 of 40, pages 13 to 40 do not exist in your file, and only another copy of the original can bring them back.
The error messages this answers
- "There was an error opening this document. The file is damaged and could not be repaired." (Adobe Reader)
- "Failed to load PDF document." (Chrome, Edge)
- "The file could not be opened. It may be damaged or use a file format that Preview does not recognise." (Mac)
- "Please wait... If this message is not eventually replaced by the proper contents of the document, your PDF viewer may not be able to display this type of document."
Keeping PDFs from getting corrupted
- Let downloads finish, and re-download anything that arrived noticeably smaller than expected.
- Wait for cloud sync to complete before opening or moving a file.
- Eject USB drives and memory cards before unplugging them.
- Keep the original of anything signed or official; re-saving a copy changes it.
Questions
How do I know if my PDF is corrupted?
Drop it on the checker. In a few seconds you get a verdict (healthy, readable with problems, damaged, unreadable, not a PDF, or password protected) and the evidence behind it.
Can a corrupted PDF be repaired?
Often, yes. Damaged indexes, truncated endings and stray bytes are repaired without losing anything. Pages whose data is gone cannot be recovered from that file.
Is my PDF uploaded to check it?
No. The check and the repair both run in your browser. Nothing is sent, which is why it is safe to check confidential documents here.
Does repair change my original file?
No. It produces a new file for you to download. If the original is digitally signed, keep it: any re-saved copy loses the signature.
Why does my PDF open in Chrome but not in another app?
Browsers quietly rebuild damaged PDFs every time they open them. Stricter apps do not. The check shows the damage the browser was hiding, and repair fixes it for good.
Is a password-protected PDF corrupted?
No, it is locked. Enter the password and the check reads every page; without it, nobody can read the content.