Thanks @sanfordwhiteman
Our landing pages are based out of pre-defined templates and the forms used inside is built out separately.
This is how our landing pages would look like:

As you can see in the above snapshot I have added a separate HTML component at the last and have defined the script as following:
<script>
MktoForms2.whenReady(function(form) {
var formEl = form.getFormElem()[0],
thankYouWindow;
form.onSubmit(function(form) {
thankYouWindow = window.open('');
});
form.onSuccess(function(vals, thankYouURL) {
thankYouWindow.document.location = 'https://Your_Guide.pdf';
window.location.replace("http://www.ourhomepage.com/");
return false;
});
});
</script>
This is working fine for me but just wanted to get this to you for your review. At the initial stage I tried adding the script within 'Edit Meta Page Tags' from the landing page properties but didn't work and then from the other threads I learned you suggested it to be added before the ending body tag and which is why I have added this as an HTML component right below the footer.
Thanks for all your help.