When copying and pasting double hyphens from Microsoft Word into the Rich Text editor, Confluence always converts them into strike-through text rather than em-dashes or en-dashes.

For example, if you type this in Word:
This text--if you can imagine--is an example of em-dashes.
Then Word converts the double-hyphens into em-dashes (because the user did not put spaces on either side of the hyphens).

But, if you copy the text from Word into Confluence, then Confluence automatically converts the text into strike-through text:
This text if you can imagine is an example of em-dashes.

Please interpret double-hyphens first, before looking for strike-through text. In this way, parenthetical statements copied from Word will be shown with en-dashes rather than strike-through text.