Have you come across this window when trying to make a change to a document?
PDF editors will usually provide the option to restrict how people can interact with the document. When you encounter the above window, it means you are trying to do something the author of the document has restricted.
You can remove these options should you have the password. Click here to learn more about document security.
Unfortunately, if you do not have access to this password, there will be no way to modify the document.