How to detect changes in any control of the form?

Instead of accessing the controls directly you can databind to a model object that implements INotifyPropertyChanged.

Whenever the user does something that causes the data in your model to change you will be notified and can take the appropriate action.

It will probably also cut down on the amount of code you need to get values in and out of the form controls.

No, I'm not aware of any event that fires whenever any control on the form changes.

My advice would be to subscribe to each event individually (if your form has so many controls that this is actually difficult to do, then you may want to re-think your UI).

If you absolutely must subscribe to changes to all controls then you might want to consider something similar to the following:

foreach (Control c in this.Controls)
{
    c.TextChanged += new EventHandler(c_ControlChanged);
}

void c_ControlChanged(object sender, EventArgs e)
{

}

Note that this wouldn't work particularly well however if you dynamically add and remove controls to the form at runtime.

Also, the TextChanged event might not be a suitable event for some control types (e.g. TextBoxes) - in this case you will need to cast and test the control type in order to be able to subscribe to the correct event, e.g.:

foreach (Control c in this.Controls)
{
    if (c is CheckBox)
    {
        ((CheckBox)c).CheckedChanged += c_ControlChanged;
    }
    else
    {
        c.TextChanged += new EventHandler(c_ControlChanged);
    }
}