Paragraph Styles and Templates
This is Word's rule regard styles associated with clauses copied from a source and pasted into a receiving document:
The receiving document controls styles.
It is as simple as that. So, if the style names associated a selected paragraph of a source document(s) is identical to a style name found in the list of style maintained by Word for the receiving document, then the style rules of the receiving document will control. Here is the impact of that rule:
(1) Let assume the style in the source document is called 'body text.' It calls for 'single spacing between paragraphs'. Now let's assume that the receiving document also has a style called 'body text' but that style is defined in the styles definitions as 'double spacing'. Double spacing will occur. Why? Because the receiving document always controls.
(2) Let's assume that a style in the source document is called "Special.' It calls for 'single spacing between paragraphs.' Now let's assume that the receiving document has no style called 'Special.' Single spacing will occur, and the style called 'Special' will be added to the receiving documents list of styles definitions.
(3) Let's now assume that a second document is added to the document under assembly and it is added after the document described in (2) above was added. And let's further say that the second document also contains a style called 'Special' but this style was defined as 'double spacing between paragraphs.' When that paragraph is poured into the document under assembly, it will come in as single space. Why? Because when the first paragraph came it, it established the definition for 'Special', and subsequent paragraphs are always controlled by existing definitions.
See Styles in the Frequently Asked Questions for a more detailed explanation of this important topic.