how to play a flash file(.swf) in u3d
Using a search engine (as the FAQ suggets) might be a good idea 
SWF is a vector animation file format, widely used to author cartoon animation that is drawn by human hands. It has much smaller file size and very high image quality for any image size, compared to general pixel based video format, such as H.264, WMV.
However, this format is not suitable for general videos shot by camera. What’s more, this format is not supported by most popular multimedia devices and players like iPhone, iPod, Android, Xbox 360, PlayStation, Windows Media Player, etc.
To play SWF files widely, follow this step by step guide at: How to Convert SWF to MP4, MOV, AVI, WMV, MKV, FLV, MP3, WAV, etc?
Hope it can help you more or less.
In order to open, edit or play SWF anywhere, a recommended solution is to convert SWF to a more popular video format like convert SWF to MP4, convert SWF to MOV, convert SWF to AVI, WMV, MPG, GIF, FLV, MKV, VOB, DV, RMVB, 3GP and etc at SWF Converter Mac/PC - Convert SWF to GIF, FLV, HTML5, MOV, MP4, MP3
Hi!
Or you can use the GAF Plugin: https://www.assetstore.unity3d.com/en/#!/content/13593 This awesome plugin supports many Adobe Flash features (including as3). Here is the website: http://gafmedia.com/
Also, here is a promo link on 500 free conversions for Unity3d 
Also you can use this extension (Flash Animation Toolset): Unity Asset Store - The Best Assets for Game Making
In order to open and play SWF, I do not recommend plugins or converters. Just use essential SWF player SWF Player for Mac: review of the best options
i use Avdshare Video Converter to Convert any SWF file to MP4, AVI, MKV, ASF, MPEG-2, MTS, ProRes, etc for using SWF on iPhone, iPad, iPod, Android, PSP, Zune, FCP, Sony Vegas, EDIUS, and any other portable device, media player or video editing programs.Convert SWF to MP4 on Mac or Windows – Avdshare