Move multiple PDF's securely

Hi all,

I am currently developing a Job which has to copy multiple PDF files to another location. At first i thought this was easy, but then my boss came and said it wasnt good enough.
Here is my setup:

I have a Table Input which collects all the document paths i need. These paths are set into Result with: Set filenames in result.
Then i have a job which moves all these files to a local folder. Next step is ZIP all these files an put it to a FTP server.

At the other side a job picks up this ZIP file and unzip it. Then this client can use the PDF's i send him.

Pretty easy right?

My boss only thinks this isnt secure enough. He likes to see if i can lock the ZIP file with a password(Static) and then my client uses this Password to unlock the zip.
He also suggested if that isnt possible; to lock every individual PDF with a password(static) and then send the individual PDF to my Client using FTP.
I tried google, i tried command line programs but nothing seems to work.

Does anyone has a suggestion how i can accomplish this? Am i missing an option in Spoon?
I am using Pentaho 5.4 and my client also uses Pentaho 5.4

Thanks in advance!