Go to the Marketing Activities area.
Select your form and click Edit Form.
Select the field you want to hide, click the Field Type drop-down and select Hidden.
With the hidden field still selected, click Edit for Autofill.
Use Default Value
selecting Use Default Value you can hard-code a specific value to always be used when this form is submitted. Enter
the Default Value
and click Save.
If you want to capture URL Parameters (Query Strings) from the page the person is on when filling out the form, you can use URL Parameters to populate your hidden field.
Select URL Parameter for Get Value Type.
Enter the Parameter Name and click Save.