Hi all,
Hope you've already found a better solution elsewhere... If not, here's an AppleScript script that may work for you. Basically, it asks the appropriate application to open the desired document, then loops waiting for the application to quit, before exiting and allowing the shutdown to proceed (hopefully).
After replacing the "..." strings at the top of the script with your specific application name (e.g., "SimpleText") and document pathname (e,g,, "Macintosh HD

ersonal:My Notes"), try saving this script as an applet (application) in the Shutdown Items folder.
-- ================================================== =======================================
try
set theAppName to "..."
set theDocumentPathname to "..."
-- Ask the app to open the document
tell application theAppName
activate
open (file theDocumentPathname)
end tell
-- Wait for the app to quit
set isAppStillOpen to true
repeat while (isAppStillOpen)
-- Yield to give time to the app, and to other apps
delay 1
-- Determine whether the app is still open
set isAppStillOpen to IsApplicationOpen(theAppName)
end repeat
on error errMsg number errNum
display dialog ("Error: (" & errNum & ") " & errMsg) buttons {"Stop"} default button 1 with icon stop
end try
-- ----------------------------------------------------------------------------------------------------------
on IsApplicationOpen(thisAppName)
set isAppOpen to false -- Initial assumption
-- Ask the Finder if the application is still running
tell application "Finder"
set theMatchingApps to (get application processes whose name is (thisAppName as string))
if ((count theMatchingApps) > 0) then
set isAppOpen to true
end if
end tell
return isAppOpen
end IsApplicationOpen
-- ================================================== =======================================
Good luck.