To secure sensitive data and information, some PDF file may have a password as a protection. If you have received a password-protected PDF, you just need to enter the password to view the file.
Some protected PDF files have other restrictions, and tools related to such features, e.g., printing, editing, copying, etc., are dimmed. When you try to print or edit such secured PDF file, you will be notified that "this document has a permission password". You can click the "Enter Password" button in the top blue highlighted notice to enter the permission password to unlock it.