Flash Decompiler can now convert Adobe Flex files.
For your convenience you can see whether it is a Flash or Flex file:
1. you'll see
or
sign above Resource panel;
2. when you click
button there will be a tooltip "Convert into FLA" or "Convert into Flex";
3. "Convert into FLA" or "Convert into Flex" tooltip will be in Main menu --> File:
Remember, that Flex files are created by Adobe Flex Builder, therefore they cannot be converted into FLA. Flash Decompiler will create a Flex Builder project, and you will need Adobe Flex Builder software to edit such project.