Hi, David. There are several ways to do this. I will list two ways here. First, you could put the field holding the attachment in a controlled access section where the formula for the controlled access section is something like @If(@Attachments>=1;“noonecanedit”;“”). This will allow users to edit the field in the section only if no attachments exist on the document. The second way of preventing editing to the attachment field is to use a computed subform where the formula says if an attachment exists on the document, then show the read only subform with the field on it. If no attachment has been attached to the document, then display the editable subform.