Export a Gmail message to Google Docs
When you open an email and click the document link, the message will be exported as a Google Document. From there you can edit it, share it, or download it as a Word, PDF, or RTF file.
In order to enable the feature, just click the Gmail Labs icon (it looks like a beaker and hangs out next to the settings link in the top right side of your Gmail homepage) and scroll down until you see the Create a Document option. Click enable and Gmail will reload with the feature enabled.