Most time you want to have a dropdown list  in your form to display ID & Name, but InfoPath form doesn’t provide your function to construct the display field. You can create a calculated field in your SharePoint list, but the problem is the form doesn’t recognized the “Calculated” column. or you can follow this blog.

But I found using SPD is much easier.

I use a variable to store the combined value and then set the value to the text field.



After uploading the document , the new field will look like


To hide the column from Editing, you need to modify it in the content type and set to hidden.

Follow here.