After you signed the purchase contract, now is the time to get your mortgage or complete the pre-approved mortgage. The purchase contract will generally include a contingency rider that gives you time to get a mortgage loan.
In addition to all the financial documents that a lender will require from you in the pre-approval process of a mortgage. Your next step is to give them a copy of the home purchase contract (could be provided by your buyer rebate broker to the lender), a title report (to indicate that the seller owns the home without any disputes of ownership, nor are there any liens on the propery), and a property appraisal (to help the lender adhere to their lending amount ratios).
The property appraisal has significant impacts if the appraisal of the home comes back lower in value. At $100 appraised value of a $100 contract purchase price, the bank can only lend $80 (or 80% of the appraised price) with your $20 down payment. At $70 appraised value of a $100 contract purchase price, the bank can only lend $56 (or 80% of the appraised price). If the seller still wants $100 for selling their home to you, then you would have to come up with $44 for the down payment.
The property appraisal is to protect the lender, because it prevents the lender in giving you a perfect diamond ring money if and when the seller is selling you a heavily flawed diamond ring that is not worth the full asking price.
Be prepared to provide every document that the lender asks of you, which they will comb through with a fine comb. Lending out a large amount of money requires complete due diligence by the lender to minimize the risk as much as possible.