There are two possible answers, neither of which fits where you are leading your question.
1. A Form is stored in between 1 and 3 files normally.
FormName.cs
FormName.Designer.cs
FormName.resx
2. A Form is a ContainerControl. The full inhertance is:
Form
ContainerControl
ScrollableControl, IContainerControl
Control, IComponent, IDisposable
Component, IDropTarget, ISynchronizeInvoke, IWin32Window, IBindableComponent, IComponent, IDisposable
MarshalByRefObject, IComponent, IDisposable