chrome.runtime.sendMessage not working in Chrome Extension

You need to change your code so that in the background.js you must change the behaviour:

console.log("Atleast reached background.js")
chrome.runtime.onMessage.addListener (
    function (request, sender, sendResponse) {
        console.log("Reached Background.js");
        if (request.Message == "getTextFile") {
            console.log("Entered IF Block");
            $.get("http://localhost:63342/Projects/StackOverflow/ChromeEXT/helloWorld1", function(response) {
                console.log(response);

                // to send back your response  to the current tab
                chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
                    chrome.tabs.sendMessage(tabs[0].id, {fileData: response}, function(response) {
                        ;
                    });
                });


            })
        }
        else {
            console.log("Did not receive the response!!!")
        }
    }
);

While for the contentscript you need to do:

console.log("Hello World!s");
$(document).ready(function() {
    console.log("DOM READY!");
    $(document.documentElement).keydown(function (e) {
        console.log("Key Has Been Pressed!");
        chrome.runtime.sendMessage({Message: "getTextFile"}, function (response) {
            ;
        })

    })
});


// accept messages from background
chrome.runtime.onMessage.addListener (function (request, sender, sendResponse) {
    alert("Contents Of Text File = " + request.fileData);
});

The sendResponse can be used as an immediate feedback not as a result of computation.

Per the text at the end of https://developer.chrome.com/extensions/messaging#simple if you return true from onMessage handler in background.js then you can call sendResponse asynchronously.