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CornerTools

Repair PDF

Fix a PDF that won't open — rebuild its structure and recover its pages, with a report of what was saved, without uploading it.

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Fixes a PDF that will not open, opens blank, or says it is damaged: a download that stopped part-way, an email attachment that came through broken, or a file a program saved badly. The tool tries the gentlest repair first, and moves to the next only when one fails or loses pages. It reports how many pages it recovered and what was wrong, and you can read the pages before downloading. The file is repaired on your device and never uploaded.

How the repair works

A PDF is a set of numbered parts, called objects: each page, its text, its fonts and its images. At the end of the file a cross-reference table says where each object starts, and a trailer says where reading begins. A file cut short loses that end first, and many programs write the list of pages there too. Most damage is to these few bytes, while the pages themselves are intact.

  1. Rebuild the structure. The file is read from start to end to rebuild the cross-reference table. Everything is kept: text, links, form fields and bookmarks.
  2. Rebuild around the pages. When the file has lost its list of pages or its trailer, the tool looks through the bytes for the pages themselves and writes a new list of them, in the order the file kept them where that survives. Text and links on the pages are kept; bookmarks and form fields, held in the part that was lost, are not. Pages that the file packs into compressed object streams cannot be found this way.
  3. Page by page. Each page that can still be read is taken out on its own and the readable ones put together, so one bad page does not cost the rest.
  4. As images. When those stages recover no page, or fewer than the file says it has, the pages are drawn by a PDF reader that recovers some files the others cannot, and saved as images at 150 DPI; the result then offers them sharper, at 300. Their text can no longer be selected or searched; Searchable PDF (OCR) makes it searchable again.

The result says which stage was used, the pages recovered of those the file says it has, and the first few problems found, in plain words. A PDF that needed nothing says so, and the download is the same PDF written out again. Before anything, the tool checks what the file really holds: a web page, ZIP file or image saved with a .pdf name is named as what it is, and an empty file is reported as empty.

Frequently asked questions

No. Whatever was in the missing part of a file cut short is gone: if a download stopped at page 6 of 10, pages 7 to 10 cannot come back. A file whose bytes were overwritten, or that was never a PDF, has nothing to recover. Download or copy it again from where it came from when you can.
The tool asks for the password, then repairs the PDF. The repaired file opens without a password; continue with Protect PDF to add one again.
No. A signature covers the file's exact bytes, and a repaired file is written anew, so the signature no longer verifies. The tool says so when the file was signed; where the signature matters, ask the sender for a new copy.
No. Your browser reads, repairs and saves the files on your device; they are not sent to CornerTools or anyone else, and neither is a password you type. To check, open the browser's developer tools at the Network tab and add a PDF: no request carries it. The PDF engine downloads from this site the first time you use it: a download to your browser, not an upload of your file.

See also

  • Unlock PDF — for a PDF that opens but asks for a password you know.
  • Searchable PDF (OCR) — to make pages recovered as images searchable again.
  • Compress PDF — when the repaired PDF is too large to send or upload.