I cannot open or download PDFs from web sites. If they are emailed to me, no issue to open. My windows Vista will not download Acrobat. Do I need Windows 7 or higher to get Acrobat that is supported on most sites?
Is has pretty likely nothing to do with Acrobat as such. Something is simply blocking "conspicuous" Internet downloads which could be as trivial as your Internet Settings in IE or some security tool you are using. Impossible to know from a distance. If you use security stuff, temporarily turn it off. in the Internet Settings you may need to allow execution of certain (unsigned) Active X's, too.