: Some PDF files are set by the author to hide toolbars upon opening. Pressing overrides this for your current session. Accidental Minimize
Sometimes the toolbar isn't missing—it’s just hidden to save screen space.
Based on user reports and technical support forums, the missing toolbar typically results from one of the following:
In Kofax Power PDF (and its predecessor, Nuance Power PDF), the acts as a master toggle for the ribbon interface.