Was the plugin needed so you could view pages that are the 'PDF' format?
It depends what Internet Browser is being used but most now include a PDF reader, so when you click on a PDF file and are asked what to open it with, choose Chrome, Firefox or whatever your preferred browser is.
I know you are on Windows 7 and the included browser (Internet Explorer) doesn't open PDF files directly. Most other browsers do though. Windows 10's included browser (Microsoft Edge) will open PDF files.
In summary, once you know about this, it most often isn't necessary to install anything additional such as an adobe plugin, Adobe Reader, Foxit Reader etc in order to open PDF files.