Adobe Reader could not open 'AdobeFlashPlayerInstaller_15_ltrosxd_aaa_aih-5.dmg' because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded).
That message looks like you are trying to open the Flash Player installer with Adobe Reader.
On Windows that means that your file association is corrupted. On Mac OS I have no idea.
Go to Control Panel > Privacy and Security and confirm that Allow Apps from Mac App Store and Identified Developers is selected.