I am currently using Ubuntu 12.04 because the latest upgrade 14.04 is not working in my system. I need to install the latest Adobe Flash Player 17 plugin, but it only allows me to install up to version 11.02, so media files cannot be opened. It says that Adobe Flash Player 17 is not compatible with my system.
Google Chrome comes with its own built-in flash player, which is currently at version 17 and regularly updated to the latest version whenever Google Chrome is updated.
For Google Chrome installation instructions see this question: How to install Chrome browser properly via command line?.
You can also install the latest version of Pepper Flash Player (the same flash player that is used in Google Chrome) in Chromium web browser directly from Ubuntu without needing to add a PPA to your software sources by following the instructions in Get latest Flash player on Ubuntu.
Alternatively, if you want to continue using Chromium, you can install the Pepper Flash plugin separately (through a PPA). This PPA installs the Pepper Flash plugin that comes with Chrome. Be sure to read the description at the top of the page (in particular, making Chromium use Pepepr Flash).