I have a C# visual studio 2005 form ...

On the form I need to programatically allow buttons to be available to be available.

e.g.
a.) available for usage if a file is open
b.) unavailable for usage if a file is not open.

Ideally I want to do something like word does -- like word, where the buttons are greyed out if you they can not be used.

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In a windows C# GUI (not web based).