When using the command-line interface (CLI) to compress with 7Zip, it may be necessary to encrypt the archive. This is easy to do with an extra switch to the command (-p).
"C:\Program Files\7-Zip\7z.exe" a E:\a-compressed-file.7z -psecretpass123 -mhe E:\important-documents\
In this example, the password is "secretpass123".
a = create an archive
p= set the password
mhe = encrypts archive headers (password required to list files within the archive)
More on 7zip encryption