I have some .fla files containing as3 code examples. I can read the .fla file into the flash professional cs5 (trial), and run the movie even, but how do I see and edit the source code? I can't seem to find any menu or window which would open the editor for the as3 code that is running it.
Just press F9 in Flash Pro. That should make the ActionScript window visible.
Also... You may need to search for the relevant embedded actionscript by selecting different frames on the timeline. Frames in the timeline with a small 'a' contain embedded actionscript.