Answers to your questions:
1. "Clicking on Submit saves the values" - Values are saved on a server. So the next time someone opens abc.html they see the values entered earlier. The user can modify the values and submit again.
2. "I don't have to type" - Any number of users. Ofcourse only one user will make changes to abc.html at one point of time.
3. "I can just open my app" - the app will be another web page. The app will be located in a remote server.
One more thing. I can't meddle with the source code of abc.html. I can only give values in the text boxes and submit them.