Encrypting Mac Files

Preview (for PDFs)

Open the PDF you want to password protect with Preview.
Go to File, then select Export, then Encrypt.
Type a password, then type it again to verify.
Save the file to ensure the password takes effect.

Keka Zip (for multiple files of any type)

Install Keka from keka.io/en
Open Keka.
Choose ZIP format type.
Enter a password.
Select use AES-256 encryption.
Drag and drop files into the Keka window.
Enter Save as Name and Save Location, then select Compress.