The first link gives you control of the Adobe Reader app instead of installing it from an third party app store.
Just an obervation on your remarks about Sony and Google, it has nothing to do with Adobe Acrobat Reader not updating on your phone.
If you download from the link above you only select which version of Android operating system is running in your mobile device and install the respective version.
You may, however, unlock and root your current device to install a customized ROM of Android or a newer version of Android OS which basically is considered a major upgrade for that device plus without all the Sony and Google bloatware ... if that is what you are asking.
There are other app stores out there such as F-Droid which are more neutral and open source oriented in terms of the content of apps that you get to choose to install in your device rather than forced to accept what gets in your device without your explicit consent