PDF files can become corrupted due to various reasons including incomplete downloads, improper system shutdowns during file access, storage media errors, virus infections, software bugs during creation or editing, and file transfer errors over networks.

While many corrupted PDF files can be successfully repaired, the possibility depends on the extent and nature of the corruption. Minor corruptions are usually completely repairable, while severely damaged files might only be partially recoverable. Professional tools have higher success rates than basic methods.

For sensitive documents, it's recommended to use offline tools to maintain privacy. If you must use online tools, choose reputable services with clear privacy policies that don't store your files permanently. For confidential documents, professional offline software is always the safer choice.

To minimize PDF corruption risks: always properly eject storage devices, maintain backup copies of important files, use reliable PDF software, avoid interrupting file transfers, regularly scan for viruses, keep your system and software updated, and consider using cloud storage with version history for important documents.