Workflow email

Hello All,

This is regarding Workflow. A mail has to be triggered to the customer with "custom messages" and a link to a FI document that the user can click on and print as a smart form.

The custom messages should be entered on the fly by the User, i.e, the User should be prompted to enter a message and the link to the FI document should automatically be on the mail before it can be sent to the customer. How can I acheieve this functionality?

Any help is appreciated !