Making Questions Read Only

Set the property to be edited to Read Only. The properties menu shows the property that is currently selected , the default property is Question Text.

Then for each question you can toggle the question between read only and updatable.

If a question is set as read only then you can optionally add an expression that makes this conditional. If you leave that expression blank then the question will always be read only. Making read only conditional only works in FieldTask but not in WebForms.