Rmfailte,
There is no "secret master password" you can use to open files that are
password protected, and whose password you've forgotten. There are "tools"
available that can crack Office document (including powerpoint, word, access
and excel) passwords for you.
There are also, along with this class of tools, ethical considerations, for
which we will leave you to your own conscience for proper guidance and use.
Google: office password recovery
Earl