Apple no longer provides security updates for its legacy QuickTime for Windows software, leaving this software vulnerable to exploitation. To safeguard Acrobat and Reader, Adobe has also deprecated support for QuickTime on Windows. Acrobat DC and Reader DC now use the built-in Windows video player to play legacy QuickTime videos—the videos embedded in PDFs created in Acrobat 9 and earlier.
When you try to play a QuickTime video inserted in a PDF, you see the following warning:
This is the default behavior. To change this behavior, choose Edit > Preferences and select Multimedia (legacy):