Recover carefully. Preserve the evidence.

When a file stops opening, the safest first step is to protect the original. Use this checklist before converting, editing or rebuilding anything.

1. Save an untouched copy

Copy the file to a different location before testing. Keep the original filename, extension, size and source information. Do not overwrite the damaged original with a guessed repair, and avoid repeated saves in the application that reports the error.

2. Check the source and transfer

Compare the byte count with a known-good copy, sender or download page. Interrupted transfers, partial synchronization and zero-byte attachments are common reasons a file will not open. A fresh authorized download may be safer than trying to rebuild missing data.

3. Identify the real format

A file extension is only a label. Use File Type Detector to inspect known signatures. A renamed archive or unexpected container format may need a different viewer, not a repair.

4. Verify only what can be verified

For ZIP files, test directory records and supported entry checksums. For PNG files, check chunk CRC values. For JSON, inspect syntax. A passing structural test is not a malware scan, authenticity guarantee or proof that all content can be decoded.

5. Repair a copy and review the differences

When a browser-local cleaning tool offers a download, save it under a new name. Validate it again, open it in a trusted application and compare meaningful content. JSONL salvage can omit invalid lines; metadata removal can discard information important to workflows.

6. Know when to stop

If the content is irreplaceable, confidential or part of a regulated record, avoid experimental repair. Consider restoring backups or using an appropriately trusted specialist. FileDoctor cannot recreate missing bytes or bypass encrypted archives.