Have you pressed on the Set Passwords
button in the Security
tab of dialog File
>Export As
>Export as PDF
?
A secondary dialog pops up with sections Set open password and Set permission password. There is a Help
button which gives the answer to your question. Even without going so far, the Security
tab already gives a summary of the security passwords (or the absence thereof).
As a general rule, always start with some navigation in the built-in help and ask here when you could not find what you were looking for.
To show the community your question has been answered, click the ✓ next to the correct answer, and “upvote” by clicking on the ^ arrow of any helpful answers. These are the mechanisms for communicating the quality of the Q&A on this site. Thanks!
In case you need clarification, edit your question (not an answer) or comment the relevant answer.