Adobe will end support for Flash Player at the end of 2020 and encourages content creators to migrate any existing Flash content to new open formats, such as HTML5, WebGL, and WebAssembly.

Check out Adobe's detailed announcement: Flash and the Future of Interactive Content.

Flash Player end-of-life (EOL) impacts playback and authoring of rich media having Flash content (*.flv and *.swf) in PDFs:

• Playback of Flash media (*.flv and *.swf) content in existing PDFs will not be supported.
• Playback, addition, or removal of Flash media (*.flv and *.swf) content embedded in 3D annotations will not be supported. You can continue to play the 3D content.
• Playback of non-Flash media (excluding *.flv and *.swf) content in PDFs will continue to be supported.
• Converting Office or HTML to PDF with embedded rich media (non-Flash content) will continue to be supported.
• Inserting or embedding rich media (non-Flash content) in PDFs will continue to be supported.