Here's the situtation!

1. A template style has to be designed.
2. Once template style is available, multiple end users will be filling up data in any docx file of their own(that may or may not be based on the template style) and send it over to the server,
3. Then the template style has to applied on all the documents. This would be done in the following way that:

a. All the styles defined in template style over-write the styles of the
user's file.
b. If after sometime, I change template style, all the documents using
template style will affected. DONE
c. The other styles in the user's file, which are not present in the template
style, will be retained.

So, how to go about it?