Password Protection not Working in Preview on Mac!

Good Morning! I've always used Adobe Pro IX to password protect my digital files.

I've gone through ALL of the steps that I usually do...but when I open the protected files in Preview on a Mac, I can copy everything!

I've password protected in PowerPoint first and then over on Adobe. I've also tried it without doing it first in PowerPoint. I'm allowed to copy everything this way!

However, if I simply password protect it in PowerPoint (without Adobe) it does ask me for a password in Preview! But, using this method alone, I can’t put a watermark on my pages or add any links!

Does anyone have any suggestions? I’m on a deadline! Thanks!