True sizes the check box or text frame according to the font size of the surrounding text. False sizes the check box or text frame according to the Size property. Read/write Boolean.
expression.AutoSize
expression Required. An expression that returns a CheckBox object.
AutoSize property as it applies to the TextFrame object.
Returns or sets a Long that represents whether a text frame is sized automatically. Read/write.
expression.AutoSize
expression Required. An expression that returns a TextFrame object.
Example
This example sets the size of the check box named "Check1" to Auto and then selects the check box.
With ActiveDocument.FormFields("Check1").CheckBox
.AutoSize = True
.Value = True
End With