Backing up a file to prevent its corruption during processing
How great is the risk that your files will be corrupted? Is there a particular reason why you think this might happen, and if so, is that cause something you can address?

Are you concerned that it is your act of processing the file that might corrupt it? If so, you may want to do the opposite of what you're doing. Don't create a backup, but instead leave the original alone and create a working copy which you discard when you're done. If something goes wrong then at least your original file is still there, untouched. 

This may sound facetious but it's not: If you don't trust your file system then it's not a good place for your application's data. How do you know that even after backing up, the file you're reading won't become corrupt as your're reading it? How do you know it wasn't already corrupt when it was backed up? How do you know that the backups won't be corrupted?

The best approach depends not only on how much you trust (or distrust) your storage but also how great the risk is if your data gets lost. If your server gets backed up regularly then that might be all the protection you need. Perhaps you could create a hash or a checksum for each file and store it with the file. When you process the file, validate that it matches the hash. That gives you about as much certainty as you could possibly want.