On the Adobe download page, you will see a checkbox that says: "Optional offer: Adobe Scan, Adobe Acrobat Online, or McAfee Security Scan."
This guide details how to download the software for free, the current system requirements, and how to get it running on your Mac. Free Download Adobe Acrobat Reader For Mac Os X
If you are running or older:
Acrobat Reader needs about 400MB of free space. Additionally, it requires space to unpack temporary files. Delete unnecessary files from your Downloads folder or empty your Trash. On the Adobe download page, you will see