Sending attachments requiring a password

SOLVED - see http://osxdaily.com/2013/05/29/password-protect-pdf-mac-os-x/

Is it possible to require a password to open an attachment? Microsoft zip files can be set up with a password but there does not appear to be a facility to do this from a Mac.

There are several file archivers with a password feature.
Go to macupdate.com (if you can stand the new look) and do a search for archiver.
TheUnarchiver, 7zip, Stuffit to name a few.