Silverlight 4 introduces a new API for accessing the clipboard through 3 static methods – GetText(), SetText(), ContainsText() . Using these methods is very simple, for example to test if there is anything on the clipboard and then paste it to a text box.
if (Clipboard.ContainsText())
{
txtText.Text = Clipboard.GetText();
}
To place text on the clipboard:
Clipboard.SetText(txtText.Text);
Silverlight can only access the clipboard from a user initiated action (such as from the mouse or keyboard) after performing this action the user is prompted to acknowledge the app is accessing the clipboard, this occurs only once per session.