What is the ruling on a real estate merchant sharing in the profits in exchange for finalizing the legal deed (sukuk shar'i) paperwork for a property and paying government fees, while also receiving a fixed amount per plot of land as profit, recovering the invested amount, and taking a plot of land as collateral?

The fact that the property owner will pay the initial investment amount means it is in the nature of a guaranteed loan. If the agreed-upon profit is in exchange for providing this guaranteed amount, then this contract is impermissible because it is a loan that brings benefit, which is usury (riba). This is further confirmed by receiving one of the properties as collateral to be sold if he fails to pay the agreed-upon amounts to collect the principal of the loan and its profit.