Wait! You have confused everything! This has nothing to do with VisualStudio. And either you use WPF or WindowsForms control. PresentationFramework.dll is WPF, the link is for the WindowsForms control.
To allow user to select all elements in wpf listbox look here: http://stackoverflow.com/questions/1030276/wpf-listbox-and-select-all
If you want to select programatically all elements, you can use the SelectedItems
] property, and add all elements from the bound source (don't forget to set multiple selection mode