We now support setting opening custom fields as offer letter and e-signature document substitution tokens. This will allow you to add opening details to your offer letter and e-signature templates for signature requests.
You can add the opening custom field token directly on the Offer Tokens page:
You can also create this directly on the opening custom field's settings page, in Substitution token section. From here, you can choose to set this token for offer letter templates, E-signature document templates, or both.