A PDF that won’t open is stressful, especially when it is an exam admit card, a payslip or a document someone needs today. Usually the file is not truly lost. A download that stopped early, an email attachment that was cut short, a USB stick pulled out too soon or a program that wrote the file badly leaves its index broken, so readers can’t find the pages even though most of them are still inside. Repair PDF rebuilds the file so it opens again.
The repair works in three steps, each more forgiving than the last. First the file’s structure is rebuilt: the cross-reference table that tells a reader where every page and image lives is recreated by scanning the whole file. Next every page is copied into a brand new, clean PDF one at a time, so a single broken page is left out instead of taking the whole document down with it. If the structure is too damaged for that, the pages are drawn one by one by a very tolerant PDF engine and saved as images, which at least gets your content back on screen and on paper.
When the first two steps work, text stays real text that you can search and copy, and images keep their quality. When the last step is needed, the pages become pictures; you can then use OCR PDF to make the text searchable again. Either way, open the repaired copy and check that every page you expect is there, because parts that were never saved into the file can’t be brought back by any tool.
The file is repaired in your browser on this device and is never uploaded, which matters because damaged files are often important ones. There is nothing to install and no account to create.
If the PDF asks for a password, it is locked rather than broken: use Unlock PDF instead. If the file is not a PDF at all, for example a Word document or a photo saved with the wrong name, open the matching converter. And when the repaired copy is larger than you need, Compress PDF can make it smaller again.