Hi,
This can be done, but it is not the easiest. Accessing this information is straightforward but saving the file with that name is considered a security issue. This means that you need a trusted function, which is a folder level javascript file that permits this activity.
For this to work you would need to install the javascript file onto every computer that would access the file. If the javascript file is missing then the script will fail (silently).
There is a long post here with several examples: XFA form with button to save file with unique filename
Good luck,
Niall