My understanding is that if they have opened datafile1 with a Username and password that is valid for datafile2 then if datafile1 needs to open datafile2 (say via a relationship) then to make life easy for the user it will open it seamlessly, with the user's original valid name and password.
If you want to set a file - say, datafile2 - to open with a default user name and password that the user does not know, then you can use the File -> File Options menu to set a default user name to log in with.
But I do not know which action takes precedence here, though I do know (to my inconvenience) that if the file database2 has already been opened (even if hidden) by database1 it will have opened with the * default * username and password.
If you are using datafile1 as simply a 'Dashboard' to launch other files from, I would suggest the following is worth a try:
- Make sure that user names and passwords are not replicated in both files
- Set datafile2 to open with a default username and password
But I have to admit I'm thrown by your comment "...thus forcing them to use datafile1". I may be missing what exactly it is you are trying to achieve.