The arrows on the left allow you to flip through pages without scrolling.
You can go directly to the page you left off by inserting the page number you want after the word 'Page.'
The - + symbols allow you to zoom in and out.
The final symbol on the right expands the page to full size.
You can scroll as well as flip through pages depending on your comfort level.
The mobile version is a normal sized pdf stripped of any web graphics to make the loading faster. It can be used for PC reading as well if you prefer scrolling to page flipping. I find the vertical layout cumbersome for reading on PC but others may not.
This is a caching problem where, although caching on the website is turned off, browsers continue to cache and on occasion fail to load pages.
To Fix This, You Can:
Avoid certain browsers such as Safari when reading these PDFs. Safari has known issues with this plugin.
Browsers that work well with this plugin are Firefox and Google Chrome.
Check the settings of your browser, and clear the cache for the page. After the cache is cleared, the PDF should load properly.
Check your Internet connection. These stories need to be read online, and if the connection times out, the story may fail to load properly.