If you wish to forward any Outlook message as a file you can use copy/paste features:
- Find and select (on message list) message that you want to forward as a file.
- Press Ctrl+C to copy selected message to clipboard.
- Hit Ctrl+N to start a new message (or Ctrl+R to respond to some other message).
- Click anywhere within main text window (or press Tab three times to get there).
- Press Ctrl+V to attach copied message as a file (paste it from Clipboard).
That's all, folks! :>
Sometimes, I need to forward message no x in my message list as a file attached in response to message no x-1 (the next coming in, since I have message list ordered by date). For this reason I use an ultra fast combination of: Ctrl+C | ↑ | Ctrl+R | Tab+Tab+Tab | Ctrl+V | Ctrl+Enter.