Preserving Style Formatting in a Merge

When you merge two documents using Insert | File, the second document is placed within the first document, and most formatting options within the first document override the formatting in what used to be the second document. If you think about it, this makes sense--after all, you are adding to the first document. It makes sense, for instance, that the margins remain the same for the document, and not as they were for the second document.

It is a similar story with styles--if both documents use styles with the same names, then inserting the second document in the first causes Word to use the style attributes of the first document, ignoring those of the second. For instance, if the first document has the Normal style defined to be 12-pt. type, and the second document has the Normal style defined to be 10-pt. type, then inserting the second document in the first will cause all the Normal-formatted paragraphs from the second document to adopt the characteristics of the Normal style in the first document. The result is that all the inserted text is now 12-pt. type.

The only way to prevent styles in the second document from adapting to the style formatting in the first document is to make sure that the second document doesn't use any of the same style names as those that exist in the first document. For instance, you could go through the second document (before the merge) and rename the styles used in the document. Make sure that you use names that you know do not exist in the first document. Then, when you do the merge, Word adds the new, renamed styles to the first document. It does this automatically, because it recognizes that the styles don't exist in the first document.