This Forms feature is included with the Diamond Package. Add-ons to other packages can be done at a costPackages only.
Settings in Forms allows you to create custom fields to add to all forms across the organization. If the standard sections in Forms doesn’t fit the need, this is the place to create those custom fields.
Form Custom Fields
Navigate to the “Settings” tab under Form Management in the left side menu panel
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When you are done adding Custom Fields, you can then add any that are not disabled to new Form Templates. See Creating Forms here