Is it private if I lock my pdf

How strong is protection of password-protected files like PDFs, Pages documents, Numbers documents which are locked with iOS or iPadOS feature to lock the files with a password? Are the files encrypted?

I’m new here


Edit:
Can any one confirm if this is reliable AES locker.

Link:

https://www.guidingtech.com/how-to-password-protect-pdf-on-iphone-ipad/

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