How to Repair a Corrupted PDF

A PDF that will not open is usually not as broken as the error message suggests. Most damage is to the index rather than the content, and an index can be rebuilt.

Repair a corrupted PDF online, step by step

1. 1Open the Repair PDF tool and add the file.
2. 2Run the repair. The document structure is rebuilt from whatever objects can be located.
3. 3Open the result and check the page count against what you expect.
4. 4Page through it — partial recovery is common and worth knowing about before you rely on it.

The repair works in two stages. It first tries a structural fix — rebuilding the cross-reference table, object numbering and trailer — and then checks that every page actually renders. If the structure is beyond saving, it falls back to recovering page by page: each page that can still be drawn is re-rendered into a fresh PDF with a searchable text layer. The message shown after the run tells you which of the two happened.

A structural fix keeps everything. A page-by-page rebuild keeps what you see and the text you can search, but the pages become images, so links and form fields do not come through. If you got the rebuild and need those, treat the result as a readable stopgap and keep looking for a clean copy.

What is actually broken

The cross-reference table is a map of where every object lives in the file. Damage it and a reader cannot find anything, even though the content is entirely intact — which is why rebuilding the map so often restores the whole document.

Password-protected files are a separate case. The Repair PDF tool cannot read an encrypted file, so it stops and asks you to remove the password with Unlock PDF first — you will need to know it — and then bring the unlocked copy back.

Before assuming corruption

1. 1Try a different reader — Chrome, Firefox and Preview are all more tolerant than some desktop applications.
2. 2Check the file size. A few hundred bytes means the download failed rather than the file being damaged.
3. 3Download it again, if it came from the web or an email.
4. 4Check it is really a PDF — open it in a text editor and look for %PDF in the first line.
5. 5Try it on another device, to rule out one broken installation.

A surprising number of "corrupted" PDFs are simply files a particular reader dislikes.

How PDFs get damaged

• Interrupted downloads and transfers.
• A USB drive removed while writing.
• Failing storage media.
• Software crashing mid-save, or a print-to-PDF driver failing before it wrote the end of the file.
• Cloud sync conflicts producing a half-written file.
• Email systems mangling an attachment in transit.

If repair does not work

Check for other copies before doing anything drastic: your email sent folder, the cloud drive's version history, a backup, the person who sent it. Cloud storage keeps previous versions for weeks and this is exactly what that feature is for. An earlier copy that opens is worth more than any amount of forensic recovery.

• If you have the source Word, Excel or design file, export a fresh PDF from it rather than fighting the damaged one.
• If the "PDF" turns out to be another kind of file with the wrong extension, open it in the program that made it and export it properly.
• If the download was interrupted, download it again — repairing the half that arrived only rescues that half.

Preventing it next time

• Let downloads, uploads and syncs finish before you open, move or rename the file.
• Eject USB drives before pulling them out.
• Use an application's own Export to PDF where it has one; it tends to be more reliable than a print-to-PDF driver.
• Keep the source document, so a damaged PDF can always be regenerated.

The repair runs in your browser, so a damaged file full of personal or work data is rebuilt on your own device rather than sent to a repair server. It is free and needs no account.