Open secured PDFs
If you receive a PDF that is protected by security features, you may need a password to open the document. Some protected documents have restrictions that prevent you from printing, editing, or copying content in the document. If a document has restricted features, any tools and menu items related to those features are dimmed.
If a document is restricted or has a special status,
the Security Settings button 
or
the Signatures button 
appear
to the left of the document window. Click the button to discover
the protection settings and determine which features are restricted.
If you have trouble opening a PDF, or if you’re restricted from using certain features, contact the author of the PDF.