Use the InitialBehaviors property to control the state of the window when it first appears. InitialBehaviors controls whether the window appears maximized, minimized, and/or pinned.
InitialBehaviors is a collection of Telerik.Web.UI.WindowBehaviors values, just like the Behaviors property. However, not all possible values make sense for InitialBehaviors. For example, if you set InitialBehaviors to "Resize", the value has no effect.
Here are the InitialBehaviors' property values that have an effect:
None - The window appears unpinned and of normal size.
Minimize - The window appears in a minimized state.
Pin - The starts out pinned.
Maximize - The window appears maximized within the parent window.
Default - The window appears both maximized and pinned. (The Maximize in this collection takes precedence over the Minimize).
You can combine InitialBehaviors values to make the window appear both pinned and either maximized or minimized. For example, if you want the window to appear minimized and pinned, set InitialBehaviors="Minimize, Pin".
The value of InitialBehaviors is not limited to the values that make up the Behaviors property. For example, if you want the window to be pinned and not to let the user unpin it, you can set InitialBehaviors="Pin" and set Behaviors to a value that does not include "Pin".
You can also set the InitialBehaviors property from the codebehind:
RadWindow1.InitialBehaviors = Telerik.Web.UI.WindowBehaviors.Pinned | Telerik.Web.UI.WindowBehaviors.Minimize;
RadWindow1.InitialBehaviors = Telerik.Web.UI.WindowBehaviors.Pinned Or Telerik.Web.UI.WindowBehaviors.Minimize