If you're distributing Flash Player within your organization you'll need to obtain a distribution license (free for the vast majority of use cases). See Adobe Flash Player Distribution | Adobe for more information.
Please note the following:
As of Windows 8.1 and Server 2012, Microsoft embeds Flash Player in IE (and Edge in Windows 10). The standalone installer will not run on these platforms. If you have Server 2012 or newer you'll need to enable Desktop Experience to enable Flash Player
To apply for a distribution license requires the use of your organization's email address. Public domain email addresses (e.g. gmail, yahoo, Hotmail, etc) will be denied.