A PDF can break in undramatic ways: a download cut off early, an email system that mangled an attachment, or software that saved an invalid structure. Viewers then show an error, blank pages or a warning that the file is damaged. Repair PDF reads the file with a tolerant engine, rebuilds its internal structure and saves a clean copy that ordinary viewers can open.
How to use Repair PDF
- Add the damaged PDF.
- If the file is password protected, enter its password when the field appears.
- Select Repair PDF.
- Open the repaired copy and page through it to confirm the content is complete.
What repair actually fixes
- The cross-reference table: Every PDF has a cross-reference table, an index that tells viewers where each page and image sits in the file. Errors in that index are the most common kind of damage, and they make strict viewers give up even when the content is intact.
- How VelloDoc rebuilds it: VelloDoc opens the file with MuPDF, which rebuilds a broken index by scanning the file, then writes a fresh, consistent structure and discards unreferenced objects.
- The fallback engine: If that engine can't read the file and Ghostscript is installed on the server, VelloDoc tries rewriting the document with Ghostscript as a second approach.
What repair can't recover
Repair works with the data that's actually in the file.
- An interrupted download: If a download stopped partway, the missing pages or images were never received and can't be rebuilt, although the pages that did arrive can often be saved.
- Content you can't decrypt: Content encrypted with a password you don't have can't be recovered either.
- Fetch it again instead: For a truncated download, fetching the file again is usually quicker and more complete than any repair.
After a successful repair
- A newly written file: A repaired file is a newly written PDF, so it often opens faster and can even be slightly smaller.
- For long-term storage: If the document is headed for long-term storage, consider converting it with PDF to PDF/A, an archival format designed to stay readable for years.
- If the file is large: If the pages are fine but the file is large, Compress PDF is a sensible next step.
- Where to read more: The guide to choosing document formats explains when PDF/A is worth using.
When people use Repair PDF
Interrupted downloads
Rescue the readable pages of a file whose download dropped out, when downloading it again isn't an option.
Attachments that won't open
Rebuild a PDF that an email system or messaging app altered in transit so it opens normally again.
Files from older software
Clean up documents written by outdated or buggy software that modern viewers flag as damaged or refuse to display.
Limitations to know
Repair PDF rebuilds a damaged structure but can't restore pages or images that are missing from the file. Severely damaged files may come back incomplete, and the Ghostscript fallback is only available when the server has Ghostscript installed.
Repair PDF: common questions
Why will my PDF not open?
Common causes are an incomplete download, an attachment altered in transit, or software that wrote an invalid file structure. Repair fixes structural problems, but it can't restore data that's missing from the file.
Will repair change how my document looks?
Normally no. Page content is kept and only the file structure is rewritten. If the Ghostscript fallback is used, the whole document is rewritten, so a quick visual check is worthwhile.
Can it fix a PDF that shows blank pages?
Sometimes. Pages that appear blank because of a broken structure often come back after repair. Pages that are blank because their content was never saved, or was cut off, can't be restored.
What happens to my file after repair?
It's processed in a temporary folder on VelloDoc's server, and that folder is deleted once the download finishes. No copy is kept.