If you can't get the password to open the file, then you may well be stuck here.
However, if this file was created by an older version of filemaker that you have had to convert with the trial copy, you may have a chance to get it open.
Older versions did not have account names. When converted, the password is used as both the account name and password in the converted file. You can open the file by simply entering the password twice, once in each box in the password dialog.
In older versions of filemaker, passwords were not case sensitive. You might get the file open by trying different capitalizations of the password.