Download in PDF or HTML a website is very easy.
Read Web Offline allows you to download web pages and store them on your mobile or tablet (including images), then you can read them without being connected, also much faster than reading online through the internal viewer android html.
This application is completely free, you will need storage space on your android, especially if you download the images.
Android 2.1+. English / Spanish / Catala
If you like this app without ADS: https://play.google.com/store/apps/details?id=vertigofreeware.readweb.noads