How to Merge Data from Opportunity into Word Document

SOLVED

Hello,

I want to achieve the following behaviour:

Within an opportunity the User clicks a button that opens an asp page. In that page he selects some documents. Now I want that if the user clicks "Save" the choosen document opens from the CRM library and Merge-Fields in that document get populated with data from the opportunity. The data also includes fields that I defined myself. Is there a way to achieve this behavior via ASP or any other CRM interface?

I tried tofind some reference in Forum discussions and the ASP-API but could not find any.

Thank you four your help!
Greetings Armin