If you have a sensitive document, then you are strongly recommended to Encrypt the document, this is not the same as simply adding a password. In Office 2007 and above and with a sufficiently strong password then the encryption is considered secure. In this case a good strong password is highly recommended, so longer than 16 characters and in a good style.
There are many versions of Microsoft Office but that latest one is Microsoft Office 2016, which, like Windows 10 updates regularly. Take a look at Microsoft Office 2016 - Wikipedia to see the latest version and when it was released. Alternatively read Version and build numbers of update channel releases for Office 365 clients for the complete list of versions. To check which version you have simply do the following: