SXPG_COMMAND_EXECUTE just runs an executable or script on the application server. You must install software on the application server that encrypts/protects pdfs, and configure SM69 accordingly.
Configuring SM69 to run an external command/script is well documented, so read the documentation. If you do not have the ability to understand the documentation, or follow instructions on installing software, then you'll need to find someone local to you who can.
I think there is a fundamental problem here, which seems quite widespread, where developers just want step-by-step instructions, but seem unable to understand the why of what they are doing, and so unable to be properly effective - always needing help from people who can read and apply documentation, and can figure things out for themselves.