This compatibility pack is what you want if you want to open, edit, and save documents, workbooks, and presentations that were created in the newer versions of Word, Excel, and PowerPoint.
They're retiring this Office Compatibility Pack in April 2018. When that happens, it will no longer be available for download and will no longer receive security updates.
If you choose to install this, be sure and read the Details, etc. before trying to download and install.
Tech changes constantly. So much so, that it's often hard to keep up with it. If you need this, better get it soon before it goes away.