Does a customer have a legal right to review their loan file and would we have to provide a copy for them to keep? If so, do they need to provide a written request or anything else?
Thank you.

You may want to consult your bank attorney on this, especially if this is a potentially adversarial situtation. For what it's worth, in my opinion the loan file is the sole property of the bank and (subject to subpoena and regulatory disclosure requirements) whether a copy will be provided to the borrower is a management decision.

I don't think it is adversarial - just that the borrower asked to see the file. Thanks for your response.

They are entitled to a copy of any document they signed or any disclosure. Otherwise I'd decline their request. Ask if they have questions about how their loan is being handled.