“The Numbers Job” is a The Thieves' Guild Faction Quest in The Elder Scrolls V: Skyrim
The Business ledger is found, typically in or near a strong box inside the shop. You need to find the box, find the ledger. Interact with the ledger and you will have the option to Forge Numbers. Simply interact with the book and you are done.
This job is active, you cannot be caught and sent to jail for any reason. If you are, the quest will fail. You cannot kill anyone inside the store, either or the quest fails.