Windows 7: Is it safe to install Adobe Reader on my PC?

Furthermore, should I directly upgrade the software or clean install?

sorry!

If you just saw a clean install of Windows go on simply download and install from the adobe site's download page. Adobe - Downloads It's about as safe as most other programs in that sense.

Typically when you need it to view a pdf file online you may see a prompt with option to bring you to or simply download and install the latest version. I've never run into any problems with having it on here.

If you are looking for an alternative reader Sumatra PDF is a good alternative. It does have some limitations however as far as creating and editing new pdf files. Sumatra PDF - Download

In most cases you will simply find adobe reader is required when going to view any pdf files like mother board manuals, specifictions, etc. online. As far as the update prompts you will see for the next latest version that will automatically remove the previous for the new.