The only requirement for this is that you are using Google Chrome. Chrome has an inbuilt pdf reader and it opens .pdf files and can also save pages as .pdf files. So whenever you hit into some interesting article that you can read later on just navigate to file -> print or hit the keyboard shortcut just change to destination to save as pdf, just a little customisation and hit save. If you are still not clear, here is a video, see this in action. To make things more readable you can use extension like Clearly.