The Adobe Acrobat Reader have been proved to be susceptible to a number of security breachs, so it is important that you upgrade your version and continue to keep it up to date.
Although not related to your website, you should be careful when accepting or viewing PDF files from other people, and therefore you should make sure the version of the reader on your PC is up to date.
If you get a prompt to upgrade your version of the Acrobat Reader then you should do so.
However, never follow any link in an email to upgrade your software, these are more likely to be a trick and will infect your PC. If in doubt go directly to the Adobe site get.adobe.com/uk/reader