From there you can type-select to get to the one you want.
On the other hand if you're trying to manage specific documents it makes more obvious sense to track the actual document path.
tell application "Microsoft Word"
set hfsPath to full name of active document
if hfsPath contains ":" then
return POSIX path of hfsPath
Now then. If you genuinely have a need to involve a variable with the Recent Menu it can be done:
set docName to "Goofy.dotx"
tell application "System Events"
set quit delay to 0
tell application process "Microsoft Word"
set frontmost to true
click menu item docName of menu 1 of menu item "Open Recent" of menu 1 of menu bar item "File" of menu bar 1