Can Prism password protect a file so only someone with the password can open it?

Microsoft Office (and some other programs) let you assign a password when you save a file. Only people who know the password can open the file. Prism does not offer this feature. 

Do note that you can zip (compress) Prism files (and any files).  Zipping programs let you include a password when you compress,  so only someone who knows that password is able to unzip the file and thus access the files within. Using password protected zip files may help you accomplish your goals..