You do not show how you copy and paste now. It should be possible to use something like this:
tell application "Word" set theData to (the clipboard as text) set the clipboard to theData end tell
This will allow you to get a text version of the clipboard data, and then replace the contents of the clipboard (which contains HTML) with plain text.
To bind a script to a function key, I recommend using Automator to create a service that runs your script, and then use the System Preferences panel to assign a key. In fact, I suspect that this whole task will be better than a service that receives text as input, rather than trying to explicitly extract it from the clipboard.
source share