The CCleaner Browser is only being offered to a limited number of users when Updating CCleaner itself. Most browsers will change your file associations when you first install them. If/when this happens then it's easy enough to change them back. For the example of PDF files: Right click on any PDF file and select 'Open With      > ' and then 'Choose another app'. Choose the application that you want to open PDFs with, then tick "Always use this App to open PDF files'.