Can a Police Officer just come to my door?

Any person, including a police officer, has your implied consent to walk onto your property for the purpose of communicating to you at your front door. If the police have a legitimate reason for communicating with you, such as responding to a call or seeking information for an investigation, then there is nothing wrong with this.

You have no obligation to answer the door when the police come knocking. There is also no obligation to speak to the police at your door, and you can end any conversation with them whenever you choose.