Hi
First, you need to create a Interaction Word Template. See this guideline for example https://yzhums.com/12509/
Then you can assign that word template to any related interaction log that is relevant.
For example: let say with every email interaction you want to send a letter that provide some details such as who is customer sales rep, etc. Then you can create a word template and define static and dynamics text. Then assign this template to Email interaction. This way anytime you use Email interaction then system generate a word document based on the template and attach to email (or in case of hard copy download PDF)