Some PDFs open without a password but stop you from printing, copying text or filling in forms. These are owner restrictions, set by whoever created the file. If it is your document, or you have permission to use it this way, you can save a copy without those restrictions. No password is needed: drop the file in and download a version you can print and copy from normally.
Tips
- Respect copyright: restrictions on published material may exist for a reason.
- Your own exported reports, invoices and statements are the typical use.
- If the file also asks for a password to open, you'll be asked for it.