Is there any reliable way to repair a file.
When I try to open it I get a message that the file is damaged or may be corrupted.
No, and if anybody tells you otherwise, they are trying to scam you. I’ve tried a ton of different tools, and none of them can fix a truely corrupted file. There are some instances when Acrobat itself will fix a file that has e.g. an incorrect xref table, but other than that, there is nothing you can do to fix a corrupt file.
What can you see at the first few lines when you open the file in a text editor like notepad?