It depends on what's inside of it !
If the .SWF contains mere video frames or refers to a separate .FLV file, then you might be able to convert such content to a more common and standard video format and publish it online. In some cases (when the content is protected or encrypted) I used a screenrecorder tool to capture a video from the playing .SWF file.
If there's interactivity involved, then it's difficult (if not impossible) to deconstruct the .SWF content and republish it in a different format. If you can retrieve the original .FLA file, then you could open it with Adobe Animate (the new name of Flash) and republish most of it as HTML5.
Oorspronkelijk geplaatst op Quora: How do I convert swf file made in macromedia flash to any other format by which I can publish online?"