I thought we stopped using password-protected ZIPs, but I don't know how to lock a PDF

Have you ever frozen up when a client asked you to "please send the PDF with a password"? Even on Yahoo! Chiebukuro, ...

No account or password required. How to receive files from others in a way that 'only you can open'

There are many situations where you need to 'have someone send you' files, not just 'send them yourself.' Collecting evidence ...