All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we thank you for being keen on seeking religious knowledge and earning your provision only through lawful means. We ask Allaah to increase yours and our insight in religion and make us all firm and steadfast on it.
As regards allowing your friend to use your real estate documents, then this is a kind of guarantee for your friend (i.e. to meet his financial obligations in case he fails to meet them). Guaranteeing is permissible; rather, it is a good act for which a person will be rewarded if he has a good intention. Since the guarantee contract is an act of donation and doing good, then it cannot be concluded for a fee. Therefore, it is not permissible for you at all to agree to take a fee for that.
Finally, it should be noted that in case your friend engages in any unlawful transaction with that bank, then it is not permissible for you to help him with maintaining a guarantee for him or with any other means, for the general meaning of the saying of Allaah (which means): {… but do not cooperate in sin and aggression.} [Quran 5:2]
Allaah Knows best.