Recover corrupted PDF files

Hello,

I'm trying to recover a folder with some critical data that was damaged or corrupted, likely by a virus. It’s a 10GB folder that contains PDF documents. None will open, and each report that the format of the file is invalid and/or does not match the extension.

I'm looking for the best tools or services, free or fee-based, that will give me the best chance of recovering at least some of this data.

Error message is attached.