https://www.pdflib.com/pdf-knowledge-base/pdf-password-security/encryption/
https://qpdf.readthedocs.io/en/stable/encryption.html
on-line nástroje: https://www.sejda.com/encrypt-pdf či https://avepdf.com/lock-pdf
off-line: https://pdfencrypt.net/ či jsignpdf
zadání hesla ve wordu ve Wordu