Repair a PDF in four steps
- Keep the original safe, then open Repair PDF.
- Add the damaged file. The tool works on a new copy.
- Run the repair and note which strategy it reports.
- Download the
-repairedcopy and check it against the original: page count, the first and last pages, and a page with a lot of text.
What breaks a PDF
A PDF is a set of objects plus an index at the end of the file that says where each one lives. Damage to that index, to a length marker, or to a compressed block can stop a viewer opening the file even though the page content is still in there. Typical causes are an incomplete download, an interrupted save or transfer, a damaged email attachment, a failing drive, and exporters with bugs. Symptoms include “the file is damaged”, “could not open”, blank pages, or a viewer that hangs.
The seven stages, from gentlest to last resort
The tool tries each strategy in order and stops at the first that produces a readable file:
| Stage | What it does | Page content |
|---|---|---|
| 1. Lenient reload | Opens the file with relaxed rules and keeps its structure | Kept where readable |
| 2. Index rebuild and length fix | Rebuilds the cross-reference index and corrects stream lengths | Kept where readable |
| 3. Compressed-stream recovery | Repairs damaged compressed streams, then rebuilds the index | Kept where readable |
| 4. Object-stream repair | Unpacks grouped objects and repairs the structure | Kept where readable |
| 5. Catalog discovery | Follows the trailer chain to find the document’s catalog, then repairs | Kept where readable |
| 6. Visual page recovery | Renders each page as an image and builds a new PDF from the images | Rebuilt as images |
| 7. Visual recovery on patched bytes | The same, after applying all the structural patches first | Rebuilt as images |
Why the last stages change what you get
Stages one to five repair the file’s internal structure and keep the original content. Stages six and seven are the last resort for files that cannot be repaired structurally: each page is drawn as an image at 200 DPI and the images are assembled into a new PDF. That produces a file that opens, but it is made of pictures, so the text is no longer selectable or searchable, links and form fields are gone, and the file can be larger. If the success message names visual recovery, treat the result as a way to read and print the document, and keep the original in case you find a better way to recover it.
If it still will not work
- “This PDF is password-protected.” Unlock it first (the unlock guide explains how), then repair the unlocked file.
- “Unable to recover this PDF.” The damage is too severe for any strategy. Re-download or re-copy the file, ask the sender for a fresh one, or look for a backup.
- It opens but looks wrong. Compare with the original and report what differs; some content may not be recoverable.
Prevent the next one
- Compare the file size with the sender’s figure after downloading, and re-download if it is smaller.
- Do not edit or save over a file while it syncs or transfers.
- Keep a copy before you convert, merge or compress; see the merge guide and the compression guide.
Privacy
Repair runs in your browser, so a damaged file, which is often a sensitive one, is not uploaded. See the private PDF tools guide for how to confirm that for any tool. Files up to 256 MB are accepted, or 128 MB on browsers that report 4 GB of memory or less.
People also ask
Common questions
Why did my PDF become corrupted?
Common causes are an incomplete download, an interrupted save or file transfer, a damaged email attachment, a failing disk or USB drive, and files produced by software with bugs. The page content may be intact even when the file’s structure is broken.
Will repair recover my text?
The first five strategies repair the file’s structure and keep the original page content, including text, where it can be read. If the tool has to use visual page recovery, the pages are rebuilt as images and text is no longer selectable.
How do I know which strategy worked?
After a successful repair the tool tells you which strategy recovered the file. A message naming visual page recovery means the pages are now images.
What if repair fails?
The message “Unable to recover this PDF” means the file is too badly damaged for any strategy. Try downloading or copying it again, ask the sender for another copy, or check for a backup.
Can it repair a password-protected PDF?
Not directly. Unlock it first with Unlock PDF, then repair the unlocked copy. Otherwise a repair could report success on a file that is still locked.
Does repair change my original file?
No. It works on a copy and leaves the original untouched, saved as the original name with -repaired added.