In the page to create new article, at the bottom in the authored on tab, how do I make the date textbox to a date field with date picker? I mean, I want it to be easy for the publisher to choose custom date.
Use Date Popup Authored module.
Date Popup Authored provides a jQuery UI datepicker for the Authored on date field found on node submission forms.
This allows content editors to pick a human-understandable date and not have to type the exact date format of the default Authored on field.