How to read content of a page from a chrome extension

Question

this is my manifest.json

{
    "name": "myApplication",
    "description": "Build an Extension!",
    "version": "1.0",
    "manifest_version": 3,
    "background": {
      "service_worker": "background.js"
    },
    "permissions": [
      "storage",
      "tabs",
    ],
    "action": {
      "default_popup": "popup.html"
    }
  }

and this the background.js

chrome.runtime.onConnect.addListener(function(port) {

     console.log("entered");


     var x = document.querySelectorAll("html");
    



  });

when i execute the extension it appears :Error in event handler: ReferenceError: document is not defined

i want to access the content of the current page, is there not something like chrome.tabs.getcurrent().document ?