Why Do Recovered Files Appear Corrupted After Data Recovery?

I recently tried recovering some deleted files from an external drive using a data recovery tool. The scan detected many files and even showed previews for some of them, but after recovering the files, several of them either wouldn’t open or appeared corrupted.

I’m wondering why this happens. Is it because the files were partially overwritten, or could it be related to file system damage or the recovery method used?

Has anyone experienced something similar?

• What usually causes recovered files to become corrupted or unusable?
• Are there any steps that can improve the chances of recovering fully usable files?