in this link
] you will get information about how you can launch your application with specific information.
After your application get launched decrypt the file and create a temporary file and then open that file using office application.
Keep checking your temporary file whether the file is as any change since the last update. Everytime user save that specific file you will get new saving time. after you received new saving time encrypt your file and store.
Also keep checking file lock issue whether the temp file is locked or not. if the file is released delete the temporary document file.