Why PDFs break
You can repair a PDF when the problem is in its structure, not its content. A PDF is made of many objects, plus a cross-reference table that tells readers where each object starts. If a download was interrupted, an email client mangled an attachment, a USB drive was pulled out mid-copy, or an app crashed while saving, that table or some objects can end up damaged.
The symptoms vary: the file won't open at all, it opens with a warning, some pages come out blank, or another tool refuses to process it. Often the actual pages are still inside the file, just hard for a reader to find.
How the repair works
ConvertirDocs tries three methods, in order. First, it rewrites the file's structure with qpdf, which can recover damaged cross-reference tables and broken objects. This is the cleanest fix, and it keeps the document as it was.
If that doesn't work, it tries a second route: loading the PDF with pdf.js, a PDF reader that is tolerant of errors, and saving it again. As a last resort, it rebuilds each page as an image. The pages look the same, but the text is no longer selectable or searchable. When this happens, ConvertirDocs tells you, so you're never surprised. You can then run “OCR PDF” on the result to make the text searchable again.
What repair can't do
Repair works with what's still in the file. If part of the content is truly gone, for example because the download stopped halfway and the last pages were never received, no tool can bring those pages back. In that case, getting the file again from its source is the only real fix.
It also can't open a PDF protected with a password you don't know. If you do know it, remove it first with “Unlock PDF”, then try the repair if the file still has problems. And if a PDF opens fine but looks wrong, like shifted text or missing fonts, that is usually a problem in how it was created, not damage that repair can undo.
Private and free
Your damaged file is processed in your browser and never leaves your device. That's useful when the broken PDF is a signed contract, a tax return or anything else you'd rather not upload to a stranger's server. There's no sign-up and no usage limit. Once repaired, you can pass the file to another tool, like “Compress PDF”, without uploading it again.