My friend has been living with her partner for over thirteen years. He is still married.
He gets a federal pension and if he dies, it goes to his wife. If he fills out forms (they
May be online) to change beneficiary to his partner, is it legal?

Is he legally separated? If so, what are the terms of the legal separation?

Some pensions - I don't know about the Fed Government - allow ONLY a married partner to receive pension benefits following the death of the former employee. I know that is how my late husband's pension was managed.

I am not at all sure that a third person (which is who your friend is) can benefit from a pension.

If anyone knows I would like to learn -

When dealing with the government they have their own rules regarding almost everything. So depending on the office and what type of plan it is etc there is no way to answer the question. I wouldn't respond by posting personal information for this type of problem. Instead have him do legwork and find out what he actually has and then see a lawyer. He really needs to finish the divorce process. In not doing so it really messes up everything.