Try turning your anti-virus off. I had this problem and turning Kaspersky off solved it. Don't forget to turn it back on again!
The title of your post refers to Adobe Flash Player, but the contents of your post refer to Adobe Reader. Which product are you having issues with?
This morning we resolved a problem that prevented Flash Player installations from completing for some of our Macintosh users.
If you encountered this problem, please delete any previously downloaded Flash Player installer and either:
1.) Download the installer again from https://get.adobe.com/flashplayer
2.) Download the stand-alone installer from http://fpdownload.macromedia.com/pub/flashplayer/latest/help/install_flash_player_osx.dmg