Encrypt the document so that opening it requires a password, with optional limits on printing and copying.
A password-protected PDF is encrypted: without the password the content cannot be read, not even by extracting the raw bytes. That is real protection, unlike a watermark. Choose a password that is long rather than clever — a phrase of four unrelated words is stronger and easier to remember than a short jumble of symbols.
Restrictions on printing, copying and editing are a polite request enforced by well-behaved software. Determined tools ignore them, so treat them as a signal of intent, not as a lock. The password is the lock.
There is no recovery. If the password is lost the document is gone — keep an unprotected copy somewhere safe while you still have one, and send the password to the recipient by a different channel than the file itself.
At least four characters are accepted, but use a long passphrase: the encryption is only as strong as the password.
Only with the password. Store it in a password manager before you close the tab.
No. Encryption prevents opening the file, not photographing a screen.