Form in a item description page?

There are several ways of adding form elements to the product pages. It actually depends what you want to do.

If the price/quantity/displayed information need to update when you select an option of the field, you need to use characteristics/variants: www.hikashop.com/support/documentation/i...html#characteristics
If you only want the price to change, it is preferable to use options:
www.hikashop.com/support/documentation/i...ct-form.html#options
If you want to have other things that dropdowns/radio buttons, like text areas, file upload, etc, you can use custom fields of the table 'item'. Price won't change and the fields will be displayed for all products by default:
www.hikashop.com/en/support/documentatio...p-field-listing.html

Characteristics/variants and options can be only on the products where you add them.
Custom fields are displayed on all of them but if you want to only display them on some products you will have to edit the code of the view like explained there:
www.hikashop.com/en/support/forum/4-how-...teristics-limit.html