A PDF can have restrictions on printing or editing while still opening without a password. If the requirement is that a recipient must enter a secret before viewing the contents, configure the opening password explicitly and test the exported file.

Use Preview on Mac with a document you are authorised to protect. Keep the editable source in its normal protected location. Decide who needs access and how the password will be retained before creating a file that may be needed months later.

Export a clearly identified protected copy

Choose File, Export and give the delivery copy a new name. Click Permissions and select Require Password To Open Document. Enter and verify the opening password. Review the separate printing and change permissions, then enter and verify the required owner password. Apply the choices and save.

Apple distinguishes the opening password from the owner password used to control permissions. The Locked checkbox beside a document title serves a different purpose: it prevents ordinary editing or deletion until unlocked. Do not use that checkbox as evidence that the contents are hidden.

Test the file that will be shared

Close the exported copy and reopen that exact file. Apple states that password changes take effect when the PDF is next opened. Confirm that access requires the opening password, then confirm that the intended password works and that every required page remains readable.

Check the filename and folder immediately before attaching or uploading it. A protected copy beside an unprotected original creates an easy selection mistake, especially when both names begin with the same words.

Use an appropriate separate channel for communicating the password and keep it out of a public filename. Protection does not correct an incorrect recipient choice or remove sensitive material already present in the pages.

If some information should never be provided to the recipient, prepare an appropriately redacted delivery document first. A person who can legitimately open a PDF can still read the content you included.

References: Apple: PDF passwords and permissions, Apple: document locking.