Preview automatically password protect PDF
I was filling out a Australian government form and I noticed a strange behavior that Preview is automatically locking the PDF file with a password.
Note: This issue does not affect all PDF file, but my guess is only when the PDF file has "form" blank spaces that can be automatically detected by the "Show Form Filling Toolbar".
It seems like the PDF file is only password-locked when the file has been modified. I can download the file from the website and open it on my computer without problem. As long as the file remains unedited, I can open and close the document without Preview locking it.
The issue happens when I make edit to the file by filling in the form, click save, and close the file window. That's when the PDF file is now locked with a password.
Another way for this issue to happen is when I'm viewing this PDF file in Safari, and making edits directly in Safari. And then when I click the download icon, I will get a password protected PDF file in my Downloads folder.
I've tried to unlock it with a blank password or my administrative password, and both didn't work.
I've included the link to download the PDF form from Australian Department of Home Affairs (https://immi.homeaffairs.gov.au/form-listing/forms/1195.pdf )
Mac mini