The Adobe Acrobat reader User Interface (UI) does not append to the basic principle that allows each new document a new window. This is unusual as all different types of User Interfaces as a standard allow a new window for a new document. Having so many tabs confined within one window or instance of adobe is extremely limiting, particularly when a document is not always afforded the screen 'real estate' when multitasking with multiple programs. Secondly, when you need to access or read multiple documents, you need to easily be able to resize and manoeuvre multiple windows easily and having them all nested within one window is extremely constraining its functionality and usability for purpose.