Create or select a form
From your HubSpot Dashboard, navigate to Contacts > Forms and either open an existing form or create a new form.
Add the necessary fields to your form by clicking the Fields tab at the top left, find your field, then drag onto the form.
Edit field options
Click on the pencil icon within the field you want to edit.
Select "Make field hidden"
From the pop-up that displays, under the Field Configuration section, you'll find a checkbox to Make field hidden. Select this checkbox.
Choose value to be passed
From your available options, choose the value which should be passed onto your contact's record upon submission. If you need, you can also add/remove property options directly within the form.
Once selected, click Done Editing.
You'll notice the blue "eye" within any fields on your form you have marked as hidden. Once you're happy with how you've set up your hidden fields to pass values, click Save form.
At the top, click preview to get a glimpse of the way your form will look on a live page. Notice that Lead Source, the hidden field on this form, does not appear on the "live" form.