Every FM file has at least one full-access username and password (unless it's been stripped out using FMPA, which I'd bet you'd remember doing).
If you're getting in without a login at work, then either it's remembered by your computer, or the File Options (File->File Options) specify that a default account should be used when logging in. If you've never messed with the security, a new file gets a username of "Admin" and a password that's blank. I'd look there and try that.
There was a behavior change with 14 related to managing security. It used to be that you had to enter a full access username and password to save changes to security (to make sure you knew one and didn't lock yourself out). Now, you're required to enter that when opening Manage Security. If the menu item isn't greyed out, that would indicate that you're already in as a full access user, but you'll need to know what that username and password is in order to get into, and then save, Manage Security.
On your iMac at work, the admin username and password may be stored in your 'Keychain'. You can look for it using the 'Keychain Access' application which is in Applications -> Utilities
If you can see it in the login keychain list, double click the entry and you will see the user account name, and then check the box to 'Show password' and after entering your login password, the FileMaker file password will be displayed.
Hi Chris and Skywillmott,
Thanks for your help! There was, in fact, a keychain password item with the password in it. Grades recovered. Happy professor.
Thanks once again,